diff --git a/ui/build/androidmk_denylist.go b/ui/build/androidmk_denylist.go
index 2ec8972..a8044df 100644
--- a/ui/build/androidmk_denylist.go
+++ b/ui/build/androidmk_denylist.go
@@ -16,6 +16,8 @@
 
 import (
 	"strings"
+
+	"android/soong/android"
 )
 
 var androidmk_denylist []string = []string{
@@ -64,3 +66,29 @@
 		}
 	}
 }
+
+// The Android.mk files in these directories are for NDK build system.
+var external_ndk_androidmks []string = []string{
+	"external/fmtlib/",
+	"external/google-breakpad/",
+	"external/googletest/",
+	"external/libaom/",
+	"external/libusb/",
+	"external/libvpx/",
+	"external/libwebm/",
+	"external/libwebsockets/",
+	"external/vulkan-validation-layers/",
+	"external/walt/",
+	"external/webp/",
+}
+
+func ignoreNdkAndroidMks(androidMks []string) []string {
+	return android.FilterListPred(androidMks, func(s string) bool {
+		for _, d := range external_ndk_androidmks {
+			if strings.HasPrefix(s, d) {
+				return false
+			}
+		}
+		return true
+	})
+}
diff --git a/ui/build/finder.go b/ui/build/finder.go
index 573df21..a899822 100644
--- a/ui/build/finder.go
+++ b/ui/build/finder.go
@@ -128,6 +128,7 @@
 
 	// Stop searching a subdirectory recursively after finding an Android.mk.
 	androidMks := f.FindFirstNamedAt(".", "Android.mk")
+	androidMks = ignoreNdkAndroidMks(androidMks)
 	blockAndroidMks(ctx, androidMks)
 	err := dumpListToFile(ctx, config, androidMks, filepath.Join(dumpDir, "Android.mk.list"))
 	if err != nil {