diff --git a/src/zstring.cpp b/src/zstring.cpp
index 14d19f46f..510ff19d7 100644
--- a/src/zstring.cpp
+++ b/src/zstring.cpp
@@ -1096,7 +1096,7 @@ void FString::ReallocBuffer (size_t newlen)
 	{ // If more than one reference, we must use a new copy
 		FStringData *old = Data();
 		AllocBuffer (newlen);
-		StrCopy (Chars, old->Chars(), old->Len);
+		StrCopy (Chars, old->Chars(), newlen < old->Len ? newlen : old->Len);
 		old->Release();
 	}
 	else