diff --git a/common/build_target.c2 b/common/build_target.c2
index ca57bec17..b0de1ae0c 100644
--- a/common/build_target.c2
+++ b/common/build_target.c2
@@ -18,6 +18,7 @@ module build_target;
 import file_list local;
 import src_loc local;
 import string_list;
+import string_map;
 import string_pool;
 import warning_flags;
 
@@ -110,7 +111,7 @@ public type Target struct @(opaque) {
     bool backend_fast;
     bool optional;
 
-    string_list.List features;
+    string_map.Map features;
     List libs;
     string_list.List exports;
     PluginList plugins;
@@ -152,10 +153,10 @@ public fn u32 Target.numFiles(const Target* t) { return t.files.getCount(); }
 
 public fn u32 Target.numAsmFiles(const Target* t) { return t.asm_files.getCount(); }
 
-public fn const string_list.List* Target.getFeatures(const Target* t) { return &t.features; }
+public fn const string_map.Map* Target.getFeatures(const Target* t) { return &t.features; }
 
 public fn void Target.addFeature(Target* t, u32 feature) {
-    t.features.add(feature);
+    t.features.addNameValue(feature, "1");
 }
 
 public fn void Target.removeFeature(Target* t, u32 feature) {
diff --git a/common/string_list.c2 b/common/string_list.c2
index c39d9bdcd..e524febd2 100644
--- a/common/string_list.c2
+++ b/common/string_list.c2
@@ -75,7 +75,7 @@ public fn void List.addStr(List* l, const char* str) {
     l.add(l.pool.addStr(str, true));
 }
 
-public fn bool List.contains(const List* l, const char* name) {
+public fn bool List.contains(const List* l, const char* name) @(unused) {
     for (u32 i=0; i<l.count; i++) {
         if (strcmp(l.pool.idx2str(l.indexes[i]), name) == 0) return true;
     }
diff --git a/common/string_map.c2 b/common/string_map.c2
new file mode 100644
index 000000000..9d20801e2
--- /dev/null
+++ b/common/string_map.c2
@@ -0,0 +1,153 @@
+/* Copyright 2022-2026 Bas van den Berg
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module string_map;
+
+import string_pool;
+import string local;
+import stdlib local;
+
+public type Map struct {
+    string_pool.Pool* pool;
+    u32* names;    // into pool
+    u32* values;   // into pool
+    u32 count;
+    u32 capacity;
+}
+
+public fn void Map.init(Map* m, string_pool.Pool* pool) {
+    memset(m, 0, sizeof(Map));
+    m.pool = pool;
+    m.resize(16);
+}
+
+public fn void Map.free(Map* m) {
+    free(m.names);
+    free(m.values);
+    m.names = nil;
+    m.values = nil;
+    m.count = 0;
+    m.capacity = 0;
+}
+
+public fn void Map.clear(Map* m) @(unused) {
+    m.count = 0;
+}
+
+fn void Map.resize(Map* m, u32 capacity) {
+    m.capacity = capacity;
+    u32* names2 = malloc(capacity * sizeof(u32));
+    u32* values2 = malloc(capacity * sizeof(u32));
+    if (m.count) {
+        memcpy(names2, m.names, m.count * sizeof(u32));
+        memcpy(values2, m.values, m.count * sizeof(u32));
+        free(m.names);
+        free(m.values);
+    }
+    m.names = names2;
+    m.values = values2;
+}
+
+public fn void Map.add(Map* m, u32 name_idx, u32 value_idx) @(unused) {
+    if (m.count == m.capacity) m.resize(m.capacity * 2);
+
+    m.names[m.count] = name_idx;
+    m.values[m.count] = value_idx;
+    m.count++;
+}
+
+// remove an index from the string map
+// return number of items removed.
+public fn u32 Map.del(Map* m, u32 name_idx) {
+    u32 j = 0;
+    u32 count = m.count;
+    for (u32 i = 0; i < count; i++) {
+        if (m.names[i] != name_idx) {
+            m.names[j] = m.names[i];
+            m.values[j] = m.values[i];
+            j++;
+        }
+    }
+    m.count = j;
+    return count - j;
+}
+
+public fn void Map.addStr(Map* m, const char* str, const char* val) @(unused) {
+    m.add(m.pool.addStr(str, true), m.pool.addStr(val, true));
+}
+
+public fn void Map.addNameValue(Map* m, u32 idx, const char* def) {
+    const char* str = m.pool.idx2str(idx);
+    u32 len;
+    const char* value = def;
+    for (len = 0; str[len]; len++) {
+        if (str[len] == '=') {
+            u32 new_idx = m.pool.add(str, len, true);
+            // reload from pool in case block was reallocated
+            value = m.pool.idx2str(idx) + len + 1;
+            idx = new_idx;
+            break;
+        }
+    }
+    m.add(idx, m.pool.addStr(value, true));
+}
+
+public fn bool Map.contains(const Map* m, const char* name, u32* indexp = nil) {
+    for (u32 i = 0; i < m.count; i++) {
+        if (!strcmp(m.pool.idx2str(m.names[i]), name)) {
+            if (indexp) *indexp = i;
+            return true;
+        }
+    }
+    return false;
+}
+
+public fn bool Map.contains_idx(const Map* m, u32 name_idx, u32* indexp = nil) @(unused) {
+    for (u32 i = 0; i < m.count; i++) {
+        if (m.names[i] == name_idx) {
+            if (indexp) *indexp = i;
+            return true;
+        }
+    }
+    return false;
+}
+
+public fn u32 Map.length(const Map* m) @(unused) {
+    return m.count;
+}
+
+public fn u32 Map.getNameIdx(const Map* m, u32 i) @(unused) {
+    return m.names[i];
+}
+
+public fn const char* Map.getName(const Map* m, u32 i) @(unused) {
+    return m.pool.idx2str(m.names[i]);
+}
+
+public fn u32 Map.getValueIdx(const Map* m, u32 i) @(unused) {
+    return m.values[i];
+}
+
+public fn const char* Map.getValue(const Map* m, u32 i) @(unused) {
+    return m.pool.idx2str(m.values[i]);
+}
+
+public fn u32* Map.getNames(const Map* m) @(unused) {
+    return m.names;
+}
+
+public fn u32* Map.getValues(const Map* m) @(unused) {
+    return m.values;
+}
diff --git a/compiler/compiler.c2 b/compiler/compiler.c2
index 7a90e2154..9f1f6170c 100644
--- a/compiler/compiler.c2
+++ b/compiler/compiler.c2
@@ -89,12 +89,13 @@ public fn void build(string_pool.Pool* auxPool,
                        build_file.Info* build_info, // can be nil
                        build_target.Target* target,
                        const Options* opts,
+                       string_list.List* features,
                        PluginHandler* pluginHandler)
 {
     Compiler c = {}
     plugin_info.Info info = {}
 
-    c.build(auxPool, sm, diags, build_info, target, opts, pluginHandler, &info);
+    c.build(auxPool, sm, diags, build_info, target, opts, features, pluginHandler, &info);
 
     if (opts.print_reports) {
         c.sm.report(opts.print_reports > 1);
@@ -174,6 +175,7 @@ fn void Compiler.build(Compiler* c,
                          build_file.Info* build_info, // can be nil
                          build_target.Target* target,
                          const Options* opts,
+                         string_list.List* features,
                          PluginHandler* pluginHandler,
                          plugin_info.Info* info)
 {
@@ -192,7 +194,7 @@ fn void Compiler.build(Compiler* c,
         c.target.disableWarnings();
         c.target.disableAsserts();
         c.removeFeature("AstStatistics");
-        c.addFeature("BOOTSTRAP", "1");
+        c.addFeature("BOOTSTRAP");
     }
 
     if (opts.no_build) {
@@ -278,16 +280,20 @@ fn void Compiler.build(Compiler* c,
     c.addGlobalDefine("SYSTEM", c.targetInfo.getSystemName());
     c.addGlobalDefine("ARCH", c.targetInfo.getArchName());
     if (c.targetInfo.intWidth == 64) {
-        c.addFeature("ARCH_64BIT", "1");
+        c.addFeature("ARCH_64BIT");
     } else {
-        c.addFeature("ARCH_32BIT", "1");
+        c.addFeature("ARCH_32BIT");
+    }
+    if (opts.asan) c.addFeature("__ASAN__");
+    if (opts.msan) c.addFeature("__MSAN__");
+    if (opts.ubsan) c.addFeature("__UBSAN__");
+
+    for (u32 i = 0; i < features.length(); i++) {
+        c.addFeature(features.get(i));
     }
-    if (opts.asan) c.addFeature("__ASAN__", "1");
-    if (opts.msan) c.addFeature("__MSAN__", "1");
-    if (opts.ubsan) c.addFeature("__UBSAN__", "1");
 
 #ifndef BOOTSTRAP
-    c.addFeature("EXPERIMENTAL", "1");
+    c.addFeature("EXPERIMENTAL");
 #endif
     c.parser = c2_parser.create(sm,
                                 diags,
@@ -489,7 +495,7 @@ fn void Compiler.findTopModule(void* arg, ast.Module* m) {
     c.mainFunc = c.analyser.findMain(m, c.main_idx);
 }
 
-fn void Compiler.addFeature(Compiler* c, const char* str, const char* value) {
+fn void Compiler.addFeature(Compiler* c, const char* str) {
     // TODO: handle value
     c.target.addFeature(c.auxPool.addStr(str, true));
 }
@@ -506,7 +512,7 @@ fn void Compiler.addGlobalDefine(Compiler* c, const char* prefix, const char* ta
         tmp[i] = (ch == '-') ? '_' : (char)ctype.toupper(ch);
     }
 
-    c.addFeature(tmp, "1");
+    c.addFeature(tmp);
 }
 
 // NOTE: paths are not 0-terminated
diff --git a/compiler/main.c2 b/compiler/main.c2
index 74ced2152..55017ba14 100644
--- a/compiler/main.c2
+++ b/compiler/main.c2
@@ -58,17 +58,20 @@ type Options struct {
     const char* output_name;
     string_list.List targets;
     string_list.List files;
+    string_list.List features;
 }
 
 fn void Options.init(Options* opts, string_pool.Pool* pool) {
     memset(opts, 0, sizeof(Options));
     opts.targets.init(pool);
     opts.files.init(pool);
+    opts.features.init(pool);
 }
 
 fn void Options.free(Options *opts) {
     opts.targets.free();
     opts.files.free();
+    opts.features.free();
 }
 
 fn void write_file_or_die(const char* filename, string_buffer.Buf* buf) {
@@ -181,6 +184,7 @@ const char[] Usage_help =
     "  -A                print Library ASTs\n"
     "  -b [file]         use specified build file\n"
     "  -d [dir]          change to [dir] first\n"
+    "  -Dfeature[=value] define global feature with optional value\n"
     "  -h                print this help\n"
     "  -i                use IR backend\n"
     "  -I                use IR backend and print generated IR\n"
@@ -326,6 +330,10 @@ fn void parse_arguments(ArgumentParser *ap, compiler.Options* comp_opts, Options
             if (arg[1] == '-') {
                 parse_long_opt(ap, arg, comp_opts, opts);
             } else {
+                const char *argarg = nil;
+                if (memchr("Ddbo", arg[1], 4)) { // need argument
+                    argarg = arg[2] ? &arg[2] : ap.getOptionArgument(arg);
+                } else
                 if (strlen(arg) != 2) {
                     switch (arg + 1) {
                     case "help":
@@ -344,6 +352,9 @@ fn void parse_arguments(ArgumentParser *ap, compiler.Options* comp_opts, Options
                 case 'A':
                     comp_opts.print_lib_ast = true;
                     break;
+                case 'D':
+                    opts.features.addStr(argarg);
+                    break;
                 case 'I':
                     opts.use_ir_backend = true;
                     comp_opts.print_ir = true;
@@ -358,10 +369,10 @@ fn void parse_arguments(ArgumentParser *ap, compiler.Options* comp_opts, Options
                     comp_opts.print_ast = true;
                     break;
                 case 'b':
-                    opts.build_file = ap.getOptionArgument(arg);
+                    opts.build_file = argarg;
                     break;
                 case 'd':
-                    opts.other_dir = ap.getOptionArgument(arg);
+                    opts.other_dir = argarg;
                     break;
                 case '?':
                 case 'h':
@@ -374,7 +385,7 @@ fn void parse_arguments(ArgumentParser *ap, compiler.Options* comp_opts, Options
                     comp_opts.print_modules = true;
                     break;
                 case 'o':
-                    opts.output_name = ap.getOptionArgument(arg);
+                    opts.output_name = argarg;
                     break;
                 case 'r':
                     comp_opts.print_reports += 1;
@@ -639,7 +650,7 @@ fn bool Context.build_target(Context* c,
         }
     }
 
-    compiler.build(c.auxPool, c.sm, c.diags, c.build_info, target, &c.comp_opts, &c.pluginHandler);
+    compiler.build(c.auxPool, c.sm, c.diags, c.build_info, target, &c.comp_opts, &c.opts.features, &c.pluginHandler);
 
     // TODO unload target-specific plugins?
     // TODO fix build_file
diff --git a/parser/c2_parser.c2 b/parser/c2_parser.c2
index f15fcb001..fcf9c79b6 100644
--- a/parser/c2_parser.c2
+++ b/parser/c2_parser.c2
@@ -27,7 +27,7 @@ import source_mgr local;
 import src_loc local;
 import stmt_list;
 import string_buffer;
-import string_list;
+import string_map;
 import string_pool;
 import token local;
 import value_type local;
@@ -59,7 +59,7 @@ public type Parser struct @(opaque) {
     diagnostics.Diags* diags;
     string_pool.Pool* pool;
     Builder* builder;
-    const string_list.List* features;
+    const string_map.Map* features;
     const keywords.Info* kwinfo;
     bool is_interface;
     bool is_generated;
@@ -85,7 +85,7 @@ public fn Parser* create(SourceMgr* sm,
                            string_pool.Pool* pool,
                            ast_builder.Builder* builder,
                            const keywords.Info* kwinfo,
-                           const string_list.List* features,
+                           const string_map.Map* features,
                            bool has_asserts)
 {
     Parser* p = calloc(1, sizeof(Parser));
diff --git a/parser/c2_tokenizer.c2 b/parser/c2_tokenizer.c2
index 70fba6651..e3f6da760 100644
--- a/parser/c2_tokenizer.c2
+++ b/parser/c2_tokenizer.c2
@@ -19,7 +19,7 @@ import constants;
 import keywords;
 import src_loc local;
 import string_buffer;
-import string_list;
+import string_map;
 import string_pool;
 import token local;
 import utf8;
@@ -271,7 +271,7 @@ public type Tokenizer struct {
     // Feature handling
     Feature[constants.MaxFeatureDepth+1] feature_stack;
     u32 feature_count;
-    const string_list.List* features;
+    const string_map.Map* features;
     bool raw_mode;  // also emit comments and invalid characters
     bool stop_at_eol; // restrict lexing to single line for preprocessor
     u8 c_mode;      // inside a module extern "C" or an extern "C" {} block
@@ -286,7 +286,7 @@ public fn void Tokenizer.init(Tokenizer* t,
                               const char* input,
                               SrcLoc loc_start,
                               const keywords.Info* kwinfo,
-                              const string_list.List* features,
+                              const string_map.Map* features,
                               ErrorFn on_error,
                               void* on_error_arg,
                               bool raw_mode)
@@ -1547,8 +1547,12 @@ fn i64 Tokenizer.parse_ppexpr(Tokenizer* t, Token *result) {
                     }
                     val.setUnsigned(t.features.contains(id));
                 } else {
-                    // TODO: use feature value
-                    val.setUnsigned(t.features.contains(id));
+                    i64 value = 0;
+                    u32 idx = 0;
+                    if (t.features.contains(id, &idx)) {
+                        value = stdlib.strtol(t.features.getValue(idx), nil, 0);
+                    }
+                    val.setSigned(value);
                 }
                 prefix = false;
                 continue;
@@ -1817,10 +1821,14 @@ fn bool Tokenizer.handle_if(Tokenizer* t, Token* result, Kind kind) {
     } else {
         /* handle Feat_ifdef, Feat_ifndef */
         if (t.lex_preproc(result) == Identifier) {
-            // TODO use feature value
             // XXX: cannot use t.features.contains_idx(result.name_idx)
             //      because t.pool and t.features.pool are different in c2c
-            if (!t.features.contains(t.pool.idx2str(result.name_idx)))
+            i64 value = 0;
+            u32 idx = 0;
+            if (t.features.contains(t.pool.idx2str(result.name_idx), &idx)) {
+                value = stdlib.strtol(t.features.getValue(idx), nil, 0);
+            }
+            if (!value)
                 top.skipping = 1;
             if (kind == Feat_ifndef)
                 top.skipping ^= 1;
diff --git a/recipe.txt b/recipe.txt
index 2777ffa01..91cee0aa7 100644
--- a/recipe.txt
+++ b/recipe.txt
@@ -20,6 +20,7 @@ set common
     common/process_utils.c2
     common/source_mgr.c2
     common/string_list.c2
+    common/string_map.c2
     common/string_utils.c2
     common/utf8.c2
     common/utils.c2
@@ -410,6 +411,7 @@ executable c2cat
     common/file/file_utils.c2
     common/file/reader.c2
     common/string_list.c2
+    common/string_map.c2
     common/utf8.c2
 
     parser/c2_tokenizer.c2
@@ -443,6 +445,7 @@ executable c2loc
     common/library_list.c2
     common/source_mgr.c2
     common/string_list.c2
+    common/string_map.c2
     common/warning_flags.c2
 
     compiler/c2recipe.c2
diff --git a/test/c_generator/defines/defines.c2t b/test/c_generator/defines/defines.c2t
index 173f83ba1..de2a0126c 100644
--- a/test/c_generator/defines/defines.c2t
+++ b/test/c_generator/defines/defines.c2t
@@ -1,15 +1,14 @@
-// @skip
 // @recipe bin
     $warnings no-unused
     $config FOO
-    $config BAR 10
+    $config BAR=10
     $backend c no-build
 
 // @file{file1}
 module test;
 import stdio local;
 
-public fn void test1() {
+public fn i32 main() {
 #ifdef FOO
     printf("FOO defined\n");
 #endif
@@ -24,12 +23,15 @@ public fn void test1() {
 #else
     printf("UNNKOWN undefined\n");
 #endif
+    return 0;
 }
 
 // @expect{atleast, cgen/build.c}
 
-
+int main(void)
+{
     printf("FOO defined\n");
     printf("BAR is 10\n");
     printf("UNNKOWN undefined\n");
-
+    return 0;
+}
diff --git a/tools/c2cat.c2 b/tools/c2cat.c2
index 4a2e0deea..aacf35b98 100644
--- a/tools/c2cat.c2
+++ b/tools/c2cat.c2
@@ -22,6 +22,7 @@ import file_utils;
 import keywords;
 import string_buffer;
 import string_list;
+import string_map;
 import string_pool;
 import number_radix;
 import token local;
@@ -256,13 +257,10 @@ public fn i32 c2cat(const char* filename, bool use_color)
     ctx.in_attributes = 0;
     u32 file_size = file.data_size();
 
-    string_list.List features;
-    features.init(ctx.pool);
+    string_map.Map features.init(ctx.pool);
     string_buffer.Buf* buf = string_buffer.create(1024, false, 0);
-    keywords.Info kwinfo;
-    kwinfo.init(ctx.pool);
-    c2_tokenizer.Tokenizer tokenizer;
-    tokenizer.init(ctx.pool, buf, ctx.input, 0, &kwinfo, &features, nil, nil, true);
+    keywords.Info kwinfo.init(ctx.pool);
+    c2_tokenizer.Tokenizer tokenizer.init(ctx.pool, buf, ctx.input, 0, &kwinfo, &features, nil, nil, true);
     ctx.tokenizer = &tokenizer;
     ctx.attr_registry.init(ctx.pool);