diff --git a/Source/CPack/cmCPackGenerator.cxx b/Source/CPack/cmCPackGenerator.cxx
index d177bae2e..f786f80e0 100644
--- a/Source/CPack/cmCPackGenerator.cxx
+++ b/Source/CPack/cmCPackGenerator.cxx
@@ -1221,7 +1221,8 @@ cmCPackGenerator::GetInstallationType(const char *projectName, const char *name)
       installType->DisplayName = installType->Name;
       }
 
-    installType->Index = this->InstallationTypes.size();
+    installType->Index = static_cast<unsigned>(
+      this->InstallationTypes.size());
     }
   return installType;
 }