diff --git a/build/tools/prebuilt-common.sh b/build/tools/prebuilt-common.sh
index a83b92a..b452629 100644
--- a/build/tools/prebuilt-common.sh
+++ b/build/tools/prebuilt-common.sh
@@ -17,6 +17,11 @@
     fi
 fi
 
+# Warn about /bin/sh ins't bash.
+if [ -z "$BASH_VERSION" ] ; then
+    echo "WARNING: The shell running this script isn't bash.  Although we try to avoid bashism in scripts, things can happen."
+fi
+
 NDK_BUILDTOOLS_ABSPATH=$(cd $NDK_BUILDTOOLS_PATH && pwd)
 
 . $NDK_BUILDTOOLS_PATH/../core/ndk-common.sh