diff --git a/rules_java_gapic/java_gapic.bzl b/rules_java_gapic/java_gapic.bzl
index 4a004b57fa..f6a16b4ea4 100644
--- a/rules_java_gapic/java_gapic.bzl
+++ b/rules_java_gapic/java_gapic.bzl
@@ -93,6 +93,8 @@ def java_gapic_library(
 
     if grpc_service_config:
         file_args_dict[grpc_service_config] = "grpc-service-config"
+    else:
+        fail("Missing a gRPC service config file")
 
     if gapic_yaml:
         file_args_dict[gapic_yaml] = "gapic-config"