diff --git a/src/libstd/num/f32.rs b/src/libstd/num/f32.rs
index c0031aa42e60..ff80a4e30535 100644
--- a/src/libstd/num/f32.rs
+++ b/src/libstd/num/f32.rs
@@ -1382,7 +1382,6 @@ mod tests {
     }
 
     #[test]
-    #[rustc_no_mir] // FIXME #27840 MIR NAN ends up negative.
     fn test_integer_decode() {
         assert_eq!(3.14159265359f32.integer_decode(), (13176795, -22, 1));
         assert_eq!((-8573.5918555f32).integer_decode(), (8779358, -10, -1));
@@ -1391,7 +1390,11 @@ mod tests {
         assert_eq!((-0f32).integer_decode(), (0, -150, -1));
         assert_eq!(INFINITY.integer_decode(), (8388608, 105, 1));
         assert_eq!(NEG_INFINITY.integer_decode(), (8388608, 105, -1));
-        assert_eq!(NAN.integer_decode(), (12582912, 105, 1));
+
+        // Ignore the "sign" (quiet / signalling flag) of NAN.
+        // It can vary between runtime operations and LLVM folding.
+        let (nan_m, nan_e, _nan_s) = NAN.integer_decode();
+        assert_eq!((nan_m, nan_e), (12582912, 105));
     }
 
     #[test]
diff --git a/src/libstd/num/f64.rs b/src/libstd/num/f64.rs
index 1a46d9a38957..b77503178708 100644
--- a/src/libstd/num/f64.rs
+++ b/src/libstd/num/f64.rs
@@ -1277,7 +1277,6 @@ mod tests {
     }
 
     #[test]
-    #[rustc_no_mir] // FIXME #27840 MIR NAN ends up negative.
     fn test_integer_decode() {
         assert_eq!(3.14159265359f64.integer_decode(), (7074237752028906, -51, 1));
         assert_eq!((-8573.5918555f64).integer_decode(), (4713381968463931, -39, -1));
@@ -1286,7 +1285,11 @@ mod tests {
         assert_eq!((-0f64).integer_decode(), (0, -1075, -1));
         assert_eq!(INFINITY.integer_decode(), (4503599627370496, 972, 1));
         assert_eq!(NEG_INFINITY.integer_decode(), (4503599627370496, 972, -1));
-        assert_eq!(NAN.integer_decode(), (6755399441055744, 972, 1));
+
+        // Ignore the "sign" (quiet / signalling flag) of NAN.
+        // It can vary between runtime operations and LLVM folding.
+        let (nan_m, nan_e, _nan_s) = NAN.integer_decode();
+        assert_eq!((nan_m, nan_e), (6755399441055744, 972));
     }
 
     #[test]