diff --git a/Sources/SakeKit/WineBuilder.swift b/Sources/SakeKit/WineBuilder.swift
index 7b015dd..b00ae6f 100644
--- a/Sources/SakeKit/WineBuilder.swift
+++ b/Sources/SakeKit/WineBuilder.swift
@@ -4,6 +4,7 @@ public enum WinePhase: String, Sendable {
     case patch
     case configure
     case sonames
+    case headers
     case make
     case install
     case verify
@@ -223,6 +224,17 @@ public struct WineBuilder: Sendable {
         onPhase(.sonames)
         try pinSonames(log: log)
 
+        // A make of its own, before anything is compiled: makedep does not follow
+        // `#include "x.idl"` when it works out what a generated header includes, so some
+        // objects miss a dependency on headers theirs include -- actxprxy_mshtml_p.o on
+        // include/exdisp.h -- and -j can compile one first. Every header it misses is in
+        // include/. See docs/wine-build.md.
+        onPhase(.headers)
+        try await runPhase(
+            .headers, make, ["-j\(jobs)", "include/all"],
+            environment: environment, log: log, onOutput: onOutput
+        )
+
         onPhase(.make)
         try await runPhase(.make, make, ["-j\(jobs)"], environment: environment, log: log, onOutput: onOutput)
 
diff --git a/Tests/SakeKitTests/WineTests.swift b/Tests/SakeKitTests/WineTests.swift
index e56eb8a..776f60a 100644
--- a/Tests/SakeKitTests/WineTests.swift
+++ b/Tests/SakeKitTests/WineTests.swift
@@ -103,7 +103,10 @@ private func makeFakeTree(
         HEADER
         cat > Makefile <<'MAKEFILE'
         all:
+        \t@test -f include/generated || { echo 'compiled before include/ was generated'; exit 1; }
         \t@echo building wine
+        include/all:
+        \t@touch include/generated
         install:
         \t@mkdir -p $$(cat prefix)/bin $$(cat prefix)/lib/wine/x86_64-unix
         \t@touch $$(cat prefix)/bin/wine
@@ -194,11 +197,28 @@ private func failure(in events: [WineEvent]) -> (reason: String, log: URL?)? {
     let phases = events.compactMap { event -> WinePhase? in
         if case .phase(let phase) = event { phase } else { nil }
     }
-    #expect(phases == [.patch, .configure, .sonames, .make, .install, .verify])
+    #expect(phases == [.patch, .configure, .sonames, .headers, .make, .install, .verify])
     #expect(events.contains(.installed(version: "Wine version 11.0")))
     #expect(builder.isBuilt)
 }
 
+@Test func includeIsGeneratedByAMakeOfItsOwnBeforeAnythingIsCompiled() async throws {
+    let paths = temporaryRoot()
+    defer { remove(paths) }
+    try makeFakeTree(in: paths)
+
+    let builder = builder(in: paths)
+    let events = await collect(builder.build())
+
+    // The fake `all` refuses to run until `include/all` has, which is the order a real
+    // build needs. See docs/wine-build.md.
+    #expect(failure(in: events) == nil)
+    let log = try String(contentsOf: builder.logURL, encoding: .utf8)
+    #expect(log.contains(
+        "=== headers /usr/bin/make -j\(ProcessInfo.processInfo.activeProcessorCount) include/all\n"
+    ))
+}
+
 @Test func wineIsBuiltOutOfTreeSoTheOnlyCopyOfItsSourceStaysClean() async throws {
     let paths = temporaryRoot()
     defer { remove(paths) }
diff --git a/docs/wine-build.md b/docs/wine-build.md
index f43eded..46f622f 100644
--- a/docs/wine-build.md
+++ b/docs/wine-build.md
@@ -149,6 +149,29 @@ clang is *not* required; the Mach-O side builds with stock Apple clang.
   `DYLD_LIBRARY_PATH`, and that does not reach Wine's child processes. sake rewrites the
   four in `include/config.h` to `@loader_path`-relative paths between configure and make;
   see `layout.md`.
+- **`include/` is generated by a make of its own before anything else is compiled.**
+  makedep works out what a widl-generated header includes from its IDL's own `import` and
+  `cpp_quote` lines, and drops an `#include "x.idl"` there (`parse_file` in
+  `tools/makedep.c`), so whatever `x.idl` imports never becomes a dependency of the objects
+  that include the header. Under `-j` one of them can be compiled before that header exists.
+
+  Reported from another machine on 2026-09-27, as
+  `dlls/actxprxy/actxprxy_mshtml.h:3287:10: fatal error: 'exdisp.h' file not found`, and not
+  reproduced on this one. `actxprxy_mshtml.idl` includes `shdeprecated.idl`, which imports
+  `exdisp.idl`. That file is CrossOver's and has no history upstream, but upstream's makedep
+  drops the same lines as of 2026-09-28, and `actxprxy_shobjidl.idl`, which upstream has too,
+  is missing six headers the same way in CrossOver's copy.
+
+  Measured in sake on 2026-09-28, against CrossOver 26.3.0's tree. It is not a matter of
+  parallelism: on a freshly configured tree, `make -j1` of
+  `dlls/actxprxy/i386-windows/actxprxy_mshtml_p.o` alone fails on `dimm.h`. A whole build
+  usually gets away with it because `libs/uuid`, which `activeds.dll` links and whose
+  `uuid.c` includes nearly every header, needs them too and is reached earlier: a serial dry
+  run generates `exdisp.h` 400 lines before the compile, and this machine's build log of
+  2026-09-20 does it 53,000 lines before. So `-j1` is no fix either; it passes by the same
+  luck. 105 IDL files in the tree include another, the headers makedep drops for them come
+  to 38, all of them in `include/`, and `include/all` generates all 38. The phase took 6.9s
+  of a 5m33s build on ten cores.
 - **Nothing x86_64 may exec an xcode-select shim.** `/usr/bin/clang`, `/usr/bin/m4` and
   their neighbours are universal shims that `dlopen` an arm64-only `libxcrun.dylib`, so
   started x86_64 they die. This bit in three unrelated places before it was recognised as one