diff --git a/simgear/xml/xmlparse.c b/simgear/xml/xmlparse.c
index c40dce07..294b73b4 100644
--- a/simgear/xml/xmlparse.c
+++ b/simgear/xml/xmlparse.c
@@ -911,7 +911,7 @@ void XML_DefaultCurrent(XML_Parser parser)
   }
 }
 
-const XML_LChar *XML_ErrorString(size_t code)
+const XML_LChar *XML_ErrorString(int code)
 {
   static const XML_LChar *message[] = {
     0,
diff --git a/simgear/xml/xmlparse.h b/simgear/xml/xmlparse.h
index 123afdf9..f2f9c9be 100644
--- a/simgear/xml/xmlparse.h
+++ b/simgear/xml/xmlparse.h
@@ -473,7 +473,7 @@ void XMLPARSEAPI
 XML_ParserFree(XML_Parser parser);
 
 /* Returns a string describing the error. */
-const XML_LChar XMLPARSEAPI *XML_ErrorString(size_t code);
+const XML_LChar XMLPARSEAPI *XML_ErrorString(int code);
 
 #ifdef __cplusplus
 }