Index: lib/builtins/fp_lib.h
===================================================================
--- lib/builtins/fp_lib.h
+++ lib/builtins/fp_lib.h
@@ -259,6 +259,18 @@
   }
 }
 
+// Iff `rep` represents the bit pattern for a NaN then return a canonical
+// representation of NaN, otherwise return `rep`.
+static __inline rep_t canonicalizeNaNRep(rep_t rep) {
+  rep_t exp = (rep & exponentMask) >> significandBits;
+  rep_t significand = (rep & significandMask);
+  if (exp == maxExponent && significand) {
+    // `rep` is a NaN
+    return qnanRep;
+  }
+  return rep;
+}
+
 // Implements logb methods (logb, logbf, logbl) for IEEE-754. This avoids
 // pulling in a libm dependency from compiler-rt, but is not meant to replace
 // it (i.e. code calling logb() should get the one from libm, not this), hence
Index: test/builtins/Unit/compiler_rt_logbf_test.c
===================================================================
--- test/builtins/Unit/compiler_rt_logbf_test.c
+++ test/builtins/Unit/compiler_rt_logbf_test.c
@@ -21,7 +21,8 @@
   fp_t crt_value = __compiler_rt_logbf(x);
   fp_t libm_value = logbf(x);
   // Compare actual rep, e.g. to avoid NaN != the same NaN
-  if (toRep(crt_value) != toRep(libm_value)) {
+  if (canonicalizeNaNRep(toRep(crt_value)) !=
+      canonicalizeNaNRep(toRep(libm_value))) {
     printf("error: in __compiler_rt_logb(%a [%X]) = %a [%X] !=  %a [%X]\n", x,
            toRep(x), crt_value, toRep(crt_value), libm_value,
            toRep(libm_value));