diff --git a/cc/arm64_device.go b/cc/arm64_device.go
index 9194c6d..8ee2bc4 100644
--- a/cc/arm64_device.go
+++ b/cc/arm64_device.go
@@ -40,6 +40,7 @@
 		// Help catch common 32/64-bit errors.
 		"-Werror=pointer-to-int-cast",
 		"-Werror=int-to-pointer-cast",
+		"-Werror=implicit-function-declaration",
 
 		"-fno-strict-volatile-bitfields",