diff --git a/avogadro/qtgui/meshgenerator.cpp b/avogadro/qtgui/meshgenerator.cpp
index 43587d695c..e829e60c3b 100644
--- a/avogadro/qtgui/meshgenerator.cpp
+++ b/avogadro/qtgui/meshgenerator.cpp
@@ -454,7 +454,7 @@ void MeshGenerator::FlyingEdgesAlgorithmPass4()
             }
 
             // Add triangles
-            const char* caseTri = m_caseTriangles[caseId]; // size 16
+            const signed char* caseTri = m_caseTriangles[caseId]; // size 16
             for(int idx = 0; caseTri[idx] != -1; idx += 3)
             {
               
diff --git a/avogadro/qtgui/meshgenerator.h b/avogadro/qtgui/meshgenerator.h
index 99dd7298fc..637de9c5ec 100644
--- a/avogadro/qtgui/meshgenerator.h
+++ b/avogadro/qtgui/meshgenerator.h
@@ -252,7 +252,7 @@ class AVOGADROQTGUI_EXPORT MeshGenerator : public QThread
    */
   static const unsigned char m_numTris[256];
   static const bool m_isCut[256][12];
-  static const char m_caseTriangles[256][16];
+  static const signed char m_caseTriangles[256][16];
   static const unsigned char m_edgeVertices[12][2];
 };