diff --git a/src/ca65/main.c b/src/ca65/main.c
index 7183ff046..d45201cad 100644
--- a/src/ca65/main.c
+++ b/src/ca65/main.c
@@ -858,7 +858,11 @@ static void OneLine (void)
             /* The line has switched the segment */
             Size = 0;
         }
-        DefSizeOfSymbol (Sym, Size);
+        /* Suppress .size Symbol if this Symbol already has a multiply-defined error,
+        ** as it will only create its own additional unnecessary error.
+        */
+        if ((Sym->Flags & SF_MULTDEF) == 0)
+            DefSizeOfSymbol (Sym, Size);
     }
 
     /* Line separator must come here */