diff --git a/src/test/run-pass/fixed_length_vec_glue.rs b/src/test/run-pass/fixed_length_vec_glue.rs
index 682ac822aa7..ab34245a8f0 100644
--- a/src/test/run-pass/fixed_length_vec_glue.rs
+++ b/src/test/run-pass/fixed_length_vec_glue.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// xfail-fast
+// xfail-fast: check-fast screws up repr paths
 
 use std::sys;
 
diff --git a/src/test/run-pass/ifmt.rs b/src/test/run-pass/ifmt.rs
index c60c97552fa..44d4386e0c5 100644
--- a/src/test/run-pass/ifmt.rs
+++ b/src/test/run-pass/ifmt.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// xfail-fast
+// xfail-fast: check-fast screws up repr paths
 
 use std::fmt;
 
diff --git a/src/test/run-pass/rec-align-u32.rs b/src/test/run-pass/rec-align-u32.rs
index 9b1f6c00056..6c4d9915d85 100644
--- a/src/test/run-pass/rec-align-u32.rs
+++ b/src/test/run-pass/rec-align-u32.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// xfail-fast
+// xfail-fast: check-fast screws up repr paths
 
 // Issue #2303
 
diff --git a/src/test/run-pass/rec-align-u64.rs b/src/test/run-pass/rec-align-u64.rs
index e4bd5c4eba7..c116353e9c9 100644
--- a/src/test/run-pass/rec-align-u64.rs
+++ b/src/test/run-pass/rec-align-u64.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// xfail-fast
+// xfail-fast: check-fast screws up repr paths
 
 // Issue #2303
 
diff --git a/src/test/run-pass/tag-align-shape.rs b/src/test/run-pass/tag-align-shape.rs
index 2075ed354bc..ee0b258fd46 100644
--- a/src/test/run-pass/tag-align-shape.rs
+++ b/src/test/run-pass/tag-align-shape.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// xfail-fast
+// xfail-fast: check-fast screws up repr paths
 
 enum a_tag {
     a_tag(u64)