diff --git a/ui/build/androidmk_denylist.go b/ui/build/androidmk_denylist.go
index e004cdcdf..9aeaf9d8e 100644
--- a/ui/build/androidmk_denylist.go
+++ b/ui/build/androidmk_denylist.go
@@ -16,8 +16,6 @@ package build
 
 import (
 	"strings"
-
-	"android/soong/android"
 )
 
 var androidmk_denylist []string = []string{
@@ -35,13 +33,13 @@ var androidmk_denylist []string = []string{
 	"toolchain/",
 }
 
-func blockAndroidMks(androidMks []string) []string {
-	return android.FilterListPred(androidMks, func(s string) bool {
+func blockAndroidMks(ctx Context, androidMks []string) {
+	for _, mkFile := range androidMks {
 		for _, d := range androidmk_denylist {
-			if strings.HasPrefix(s, d) {
-				return false
+			if strings.HasPrefix(mkFile, d) {
+				ctx.Fatalf("Found blocked Android.mk file: %s. "+
+					"Please see androidmk_denylist.go for the blocked directories and contact build system team if the file should not be blocked.", mkFile)
 			}
 		}
-		return true
-	})
+	}
 }
diff --git a/ui/build/finder.go b/ui/build/finder.go
index a114079ff..573df21d9 100644
--- a/ui/build/finder.go
+++ b/ui/build/finder.go
@@ -128,7 +128,7 @@ func FindSources(ctx Context, config Config, f *finder.Finder) {
 
 	// Stop searching a subdirectory recursively after finding an Android.mk.
 	androidMks := f.FindFirstNamedAt(".", "Android.mk")
-	androidMks = blockAndroidMks(androidMks)
+	blockAndroidMks(ctx, androidMks)
 	err := dumpListToFile(ctx, config, androidMks, filepath.Join(dumpDir, "Android.mk.list"))
 	if err != nil {
 		ctx.Fatalf("Could not export module list: %v", err)