diff --git a/src/libcore/os.rs b/src/libcore/os.rs
index a6e95af45eaf..aa4a6feb76f7 100644
--- a/src/libcore/os.rs
+++ b/src/libcore/os.rs
@@ -222,7 +222,7 @@ pub fn env() -> ~[(~str,~str)] {
                 log(debug,
                     fmt!("splitting: len: %u",
                     vs.len()));
-                assert vs.len() == 2;
+                fail_unless!(vs.len() == 2);
                 pairs.push((copy vs[0], copy vs[1]));
             }
             pairs
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index 9f8ddc92a772..e622b0c4ca32 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -463,11 +463,11 @@ pub mod ptr_tests {
                 log(debug,
                     fmt!("test_ptr_array_each e: %s, a: %s",
                          expected, actual));
-                assert actual == expected;
+                fail_unless!(actual == expected);
                 ctr += 1;
                 iteration_count += 1;
             });
-            assert iteration_count == 3u;
+            fail_unless!(iteration_count == 3u);
         }
     }
     #[test]
@@ -495,11 +495,11 @@ pub mod ptr_tests {
                 log(debug,
                     fmt!("test_ptr_array_each e: %s, a: %s",
                          expected, actual));
-                assert actual == expected;
+                fail_unless!(actual == expected);
                 ctr += 1;
                 iteration_count += 1;
             });
-            assert iteration_count == 3;
+            fail_unless!(iteration_count == 3);
         }
     }
     #[test]