diff --git a/compiler/semantic/sql.go b/compiler/semantic/sql.go
index acc3c0471..eecf7eaa9 100644
--- a/compiler/semantic/sql.go
+++ b/compiler/semantic/sql.go
@@ -720,10 +720,21 @@ func (t *translator) resolveOrdinalOuter(ts tableScope, n ast.Node, prefix strin
 func dedup(scores map[string]int, s string) string {
 	cnt := scores[s]
 	scores[s] = cnt + 1
-	if cnt != 0 {
-		s = fmt.Sprintf("%s_%d", s, cnt)
+	if cnt == 0 {
+		return s
+	}
+	// Suffix duplicate names with "_<n>", but skip any candidate that is
+	// already taken by another column (explicit or previously generated) so
+	// the projected record cannot end up with two identical field names, which
+	// would panic in MustLookupTypeRecord (e.g. "SELECT 1 AS x, 2 AS x, 3 AS x_1").
+	for {
+		candidate := fmt.Sprintf("%s_%d", s, cnt)
+		if scores[candidate] == 0 {
+			scores[candidate] = 1
+			return candidate
+		}
+		cnt++
 	}
-	return s
 }
 
 func valuesExpr(e sem.Expr, seq sem.Seq) sem.Seq {
diff --git a/compiler/ztests/sql/select-dup-alias-collision.yaml b/compiler/ztests/sql/select-dup-alias-collision.yaml
new file mode 100644
index 000000000..557e4f6bb
--- /dev/null
+++ b/compiler/ztests/sql/select-dup-alias-collision.yaml
@@ -0,0 +1,9 @@
+script: |
+  super compile -C -O "select 1 as x, 2 as x, 3 as x_1"
+
+outputs:
+  - name: stdout
+    data: |
+      null
+      | values {x:1,x_1:2,x_1_1:3}
+      | output main