diff --git a/rust/proc_macro.go b/rust/proc_macro.go
index c217959..804d79f 100644
--- a/rust/proc_macro.go
+++ b/rust/proc_macro.go
@@ -63,6 +63,12 @@
 		&procMacro.Properties)
 }
 
+func (procMacro *procMacroDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
+	flags = procMacro.baseCompiler.compilerFlags(ctx, flags)
+	flags.RustFlags = append(flags.RustFlags, "--extern proc_macro")
+	return flags
+}
+
 func (procMacro *procMacroDecorator) compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path {
 	fileName := procMacro.getStem(ctx) + ctx.toolchain().ProcMacroSuffix()
 	outputFile := android.PathForModuleOut(ctx, fileName)