diff --git a/src/common/dpycmn.cpp b/src/common/dpycmn.cpp
index 8797f81ecb..81a2a8e85c 100644
--- a/src/common/dpycmn.cpp
+++ b/src/common/dpycmn.cpp
@@ -44,7 +44,7 @@ const wxVideoMode wxDefaultVideoMode;
 wxDisplayBase::wxDisplayBase(size_t index)
              : m_index (index)
 {
-    wxASSERT_MSG( m_index < GetCount(),
+    wxASSERT_MSG( m_index >= 0 && m_index < GetCount(),
                     wxT("An invalid index was passed to wxDisplay") );
 }