diff --git a/lib/libGDSII.h b/lib/libGDSII.h
index 569d903..ee9243f 100644
--- a/lib/libGDSII.h
+++ b/lib/libGDSII.h
@@ -230,7 +230,7 @@ void ClearGDSIICache();
 bool DumpGDSIIFile(const char *FileName);
 void WriteGMSHEntity(Entity E, int Layer, const char *geoFileName, FILE **pgeoFile,
                      const char *ppFileName=0, FILE **pppFile=0);
-void WriteGMSHFile(EntityTable ETable, iVec Layers, char *FileBase, bool SeparateLayers=false);
+void WriteGMSHFile(EntityTable ETable, iVec Layers, const char *FileBase, bool SeparateLayers=false);
 
 } /* namespace libGDSII */