diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
index 69a8890..a028a5d 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
@@ -390,6 +390,9 @@
     // anyway. Not having to look at them here saves us from requiring and ArtifactExpander, which
     // actionExecutionContext doesn't have at this point. This only works as long as mandatory
     // inputs do not contain headers that are built into a module.
+    for (Artifact source : getIncludeScannerSources()) {
+      undeclaredHeaders.remove(source);
+    }
     for (Artifact header : ccCompilationContext.getDeclaredIncludeSrcs()) {
       undeclaredHeaders.remove(header);
     }