diff --git a/HISTORY.TXT b/HISTORY.TXT
index b4126aee88..2e849c34c1 100644
--- a/HISTORY.TXT
+++ b/HISTORY.TXT
@@ -14,6 +14,8 @@ For a complete change history, please see the Git log comments.
 Current Version (future 6.0.4, GIT branch-6-0):
 -----------------------------------------------
 
+- Fixed "msGetMarkerSize() called on unloaded pixmap symbol" in mapsymbol.c (#4225)
+
 - Fixed PHP MapScript support for PHP 5.4 (#4309)
 
 - Fix msOGREscapeSQLParam could return random data (#4335)
diff --git a/mapsymbol.c b/mapsymbol.c
index 164a0acf36..f9dcb20a35 100644
--- a/mapsymbol.c
+++ b/mapsymbol.c
@@ -601,6 +601,10 @@ int msGetMarkerSize(symbolSetObj *symbolset, styleObj *style, int *width, int *h
   }
   
   symbol = symbolset->symbol[style->symbol];
+  if (symbol->type == MS_SYMBOL_PIXMAP && !symbol->pixmap_buffer) {
+    if (MS_SUCCESS != msPreloadImageSymbol(MS_MAP_RENDERER(symbolset->map), symbol))
+        return MS_FAILURE;
+  }
   if(style->size == -1) {
       size = MS_NINT( msSymbolGetDefaultSize(symbol) * scalefactor );
   }