diff --git a/src/Magnum/DebugTools/CompareImage.cpp b/src/Magnum/DebugTools/CompareImage.cpp
index 167b63b9e..d7c3fe370 100644
--- a/src/Magnum/DebugTools/CompareImage.cpp
+++ b/src/Magnum/DebugTools/CompareImage.cpp
@@ -396,6 +396,8 @@ void printPixelDeltas(Debug& out, Containers::ArrayView<const Float> delta, Pixe
     }
 }
 
+namespace {
+
 enum class Result: UnsignedByte {
     PluginLoadFailed = 1,
     ActualImageLoadFailed,
@@ -410,6 +412,8 @@ enum class Result: UnsignedByte {
     VerboseMessage
 };
 
+}
+
 class ImageComparatorBase::State {
     public:
         explicit State(PluginManager::Manager<Trade::AbstractImporter>* importerManager, PluginManager::Manager<Trade::AbstractImageConverter>* converterManager, Float maxThreshold, Float meanThreshold): _importerManager{importerManager}, _converterManager{converterManager}, maxThreshold{maxThreshold}, meanThreshold{meanThreshold} {}