diff --git a/src/libcore/str.rs b/src/libcore/str.rs
index 0a44d1fb414..2c7c55418da 100644
--- a/src/libcore/str.rs
+++ b/src/libcore/str.rs
@@ -1329,9 +1329,7 @@ fn escape_char(c: char) -> str {
       '\n' { "\\n" }
       '\t' { "\\t" }
       '\r' { "\\r" }
-      // FIXME: uncomment this when extfmt is moved to core
-      // in a snapshot.
-      // '\x00' to '\x1f' { #fmt["\\x%02x", c as uint] }
+      '\x00' to '\x1f' { #fmt["\\x%02x", c as uint] }
       v { from_char(c) }
     }
 }
@@ -2297,6 +2295,11 @@ mod tests {
         assert(escape("abc\"def") == "abc\\\"def");
     }
 
+    #[test]
+    fn test_escape_char() {
+        assert escape_char('\x1f') == "\\x1f";
+    }
+
     #[test]
     fn test_map() {
         assert "" == map("", char::to_upper);