diff --git a/Source/cmFileAPICodemodel.cxx b/Source/cmFileAPICodemodel.cxx
index ff11f4a797..efe1ab6fb8 100644
--- a/Source/cmFileAPICodemodel.cxx
+++ b/Source/cmFileAPICodemodel.cxx
@@ -874,6 +874,7 @@ Json::Value DirectoryObject::DumpInstallers()
 
 Json::Value DirectoryObject::DumpInstaller(cmInstallGenerator* gen)
 {
+  assert(gen);
   Json::Value installer = Json::objectValue;
 
   // Exclude subdirectory installers.  They are implementation details.