diff --git a/objc/runtime.h b/objc/runtime.h
index 3818330..f8abc8a 100644
--- a/objc/runtime.h
+++ b/objc/runtime.h
@@ -311,7 +311,11 @@ const char *sel_getType_np(SEL aSel) OBJC_NONPORTABLE;
 
 /**
  * Enumerates all of the type encodings associated with a given selector name
- * (up to a specified limit).
+ * (up to a specified limit).  This function returns the number of types that
+ * exist for a specific selector, but only copies up to count of them into the
+ * array passed as the types argument.  This allows you to call the function
+ * once with a relatively small on-stack buffer and then only call it again
+ * with a heap-allocated buffer if there is not enough space.
  */
 unsigned sel_copyTypes_np(const char *selName, const char **types, unsigned count) OBJC_NONPORTABLE;
 
diff --git a/selector_table.c b/selector_table.c
index ca51a52..fed5e5e 100644
--- a/selector_table.c
+++ b/selector_table.c
@@ -395,9 +395,13 @@ unsigned sel_copyTypes_np(const char *selName, const char **types, unsigned coun
 	}
 
 	unsigned found = 0;
-	while (NULL != l && found<count)
+	while (NULL != l) 
 	{
-		types[found++] = l->value;
+		if (found<count)
+		{
+			types[found] = l->value;
+		}
+		found++;
 		l = l->next;
 	}
 	return found;