diff --git a/src/RageSurface_Load_XPM.cpp b/src/RageSurface_Load_XPM.cpp
index 7b12aead04..03f36c3b0b 100644
--- a/src/RageSurface_Load_XPM.cpp
+++ b/src/RageSurface_Load_XPM.cpp
@@ -96,7 +96,7 @@ RageSurface *RageSurface_Load_XPM( char * const *xpm, RString &error )
 		int32_t *p32 = (int32_t *) p;
 		for( int x = 0; x < width; ++x )
 		{
-			RString color_name = row.substr( x*color_length, color_length );
+			RString color_name = row.substr( static_cast<size_t>(x) * color_length, color_length );
 			std::map<RString, int>::const_iterator it;
 			it = name_to_color.find( color_name );
 			if( it == name_to_color.end() )