diff --git a/GeneratorInterface/Core/plugins/ExternalGeneratorFilter.cc b/GeneratorInterface/Core/plugins/ExternalGeneratorFilter.cc
index 9a8960f10fdb7..aafe19453141d 100644
--- a/GeneratorInterface/Core/plugins/ExternalGeneratorFilter.cc
+++ b/GeneratorInterface/Core/plugins/ExternalGeneratorFilter.cc
@@ -62,7 +62,7 @@ namespace externalgen {
         {
           auto nlines = std::to_string(std::count(iConfig.begin(), iConfig.end(), '\n'));
           auto result = fwrite(nlines.data(), sizeof(char), nlines.size(), pipe_);
-          assert(result = nlines.size());
+          assert(result == nlines.size());
           result = fwrite(iConfig.data(), sizeof(char), iConfig.size(), pipe_);
           assert(result == iConfig.size());
           fflush(pipe_);