diff -Naurd mpfr-4.0.1-a/PATCHES mpfr-4.0.1-b/PATCHES
--- mpfr-4.0.1-a/PATCHES	2018-04-27 12:52:13.875783093 +0000
+++ mpfr-4.0.1-b/PATCHES	2018-04-27 12:52:13.911782747 +0000
@@ -0,0 +1 @@
+cmp_q-special
diff -Naurd mpfr-4.0.1-a/VERSION mpfr-4.0.1-b/VERSION
--- mpfr-4.0.1-a/VERSION	2018-04-27 12:50:10.624974512 +0000
+++ mpfr-4.0.1-b/VERSION	2018-04-27 12:52:13.911782747 +0000
@@ -1 +1 @@
-4.0.1-p4
+4.0.1-p5
diff -Naurd mpfr-4.0.1-a/src/gmp_op.c mpfr-4.0.1-b/src/gmp_op.c
--- mpfr-4.0.1-a/src/gmp_op.c	2018-01-09 12:30:58.000000000 +0000
+++ mpfr-4.0.1-b/src/gmp_op.c	2018-04-27 12:52:13.899782862 +0000
@@ -452,11 +452,15 @@
   mpfr_prec_t p;
   MPFR_SAVE_EXPO_DECL (expo);
 
-  if (MPFR_UNLIKELY (mpq_denref (q) == 0))
+  if (MPFR_UNLIKELY (mpz_sgn (mpq_denref (q)) == 0))
     {
       /* q is an infinity or NaN */
-      mpfr_init2 (t, 2);
+      mpfr_flags_t old_flags;
+
+      mpfr_init2 (t, MPFR_PREC_MIN);
+      old_flags = __gmpfr_flags;
       mpfr_set_q (t, q, MPFR_RNDN);
+      __gmpfr_flags = old_flags;
       res = mpfr_cmp (x, t);
       mpfr_clear (t);
       return res;
diff -Naurd mpfr-4.0.1-a/src/mpfr.h mpfr-4.0.1-b/src/mpfr.h
--- mpfr-4.0.1-a/src/mpfr.h	2018-04-27 12:50:10.620974551 +0000
+++ mpfr-4.0.1-b/src/mpfr.h	2018-04-27 12:52:13.907782785 +0000
@@ -27,7 +27,7 @@
 #define MPFR_VERSION_MAJOR 4
 #define MPFR_VERSION_MINOR 0
 #define MPFR_VERSION_PATCHLEVEL 1
-#define MPFR_VERSION_STRING "4.0.1-p4"
+#define MPFR_VERSION_STRING "4.0.1-p5"
 
 /* User macros:
    MPFR_USE_FILE:        Define it to make MPFR define functions dealing
diff -Naurd mpfr-4.0.1-a/src/version.c mpfr-4.0.1-b/src/version.c
--- mpfr-4.0.1-a/src/version.c	2018-04-27 12:50:10.624974512 +0000
+++ mpfr-4.0.1-b/src/version.c	2018-04-27 12:52:13.911782747 +0000
@@ -25,5 +25,5 @@
 const char *
 mpfr_get_version (void)
 {
-  return "4.0.1-p4";
+  return "4.0.1-p5";
 }
diff -Naurd mpfr-4.0.1-a/tests/tgmpop.c mpfr-4.0.1-b/tests/tgmpop.c
--- mpfr-4.0.1-a/tests/tgmpop.c	2018-01-09 12:30:58.000000000 +0000
+++ mpfr-4.0.1-b/tests/tgmpop.c	2018-04-27 12:52:13.899782862 +0000
@@ -307,16 +307,39 @@
   mpfr_init2 (z, MPFR_PREC_MIN);
   mpq_init (y);
 
-  /* check the erange flag when x is NaN */
+  /* Check the flags when x is NaN: the erange flags must be set, and
+     only this one. */
   mpfr_set_nan (x);
   mpq_set_ui (y, 17, 1);
-  mpfr_clear_erangeflag ();
+  mpfr_clear_flags ();
   res1 = mpfr_cmp_q (x, y);
-  if (res1 != 0 || mpfr_erangeflag_p () == 0)
+  if (res1 != 0 || __gmpfr_flags != MPFR_FLAGS_ERANGE)
     {
       printf ("Error for mpfr_cmp_q (NaN, 17)\n");
       printf ("Return value: expected 0, got %d\n", res1);
-      printf ("Erange flag: expected set, got %d\n", mpfr_erangeflag_p ());
+      printf ("Expected flags:");
+      flags_out (MPFR_FLAGS_ERANGE);
+      printf ("Got flags:     ");
+      flags_out (__gmpfr_flags);
+      exit (1);
+    }
+
+  /* Check the flags when y is NaN: the erange flags must be set, and
+     only this one. */
+  mpfr_set_ui (x, 42, MPFR_RNDN);
+  /* A NaN rational is represented by 0/0 (MPFR extension). */
+  mpz_set_ui (mpq_numref (y), 0);
+  mpz_set_ui (mpq_denref (y), 0);
+  mpfr_clear_flags ();
+  res1 = mpfr_cmp_q (x, y);
+  if (res1 != 0 || __gmpfr_flags != MPFR_FLAGS_ERANGE)
+    {
+      printf ("Error for mpfr_cmp_q (42, NaN)\n");
+      printf ("Return value: expected 0, got %d\n", res1);
+      printf ("Expected flags:");
+      flags_out (MPFR_FLAGS_ERANGE);
+      printf ("Got flags:     ");
+      flags_out (__gmpfr_flags);
       exit (1);
     }
 
@@ -341,6 +364,55 @@
             }
         }
     }
+
+  /* check for y = 1/0 */
+  mpz_set_ui (mpq_numref (y), 1);
+  mpz_set_ui (mpq_denref (y), 0);
+  mpfr_set_ui (x, 1, MPFR_RNDN);
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) < 0);
+  mpfr_set_inf (x, -1);
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) < 0);
+  mpfr_set_inf (x, +1);
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  mpfr_set_nan (x);
+  mpfr_clear_erangeflag ();
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  MPFR_ASSERTN(mpfr_erangeflag_p ());
+
+  /* check for y = -1/0 */
+  mpz_set_si (mpq_numref (y), -1);
+  mpz_set_ui (mpq_denref (y), 0);
+  mpfr_set_ui (x, 1, MPFR_RNDN);
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) > 0);
+  mpfr_set_inf (x, -1);
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  mpfr_set_inf (x, +1);
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) > 0);
+  mpfr_set_nan (x);
+  mpfr_clear_erangeflag ();
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  MPFR_ASSERTN(mpfr_erangeflag_p ());
+
+  /* check for y = 0/0 */
+  mpz_set_ui (mpq_numref (y), 0);
+  mpz_set_ui (mpq_denref (y), 0);
+  mpfr_set_ui (x, 1, MPFR_RNDN);
+  mpfr_clear_erangeflag ();
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  MPFR_ASSERTN(mpfr_erangeflag_p ());
+  mpfr_set_inf (x, -1);
+  mpfr_clear_erangeflag ();
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  MPFR_ASSERTN(mpfr_erangeflag_p ());
+  mpfr_set_inf (x, +1);
+  mpfr_clear_erangeflag ();
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  MPFR_ASSERTN(mpfr_erangeflag_p ());
+  mpfr_set_nan (x);
+  mpfr_clear_erangeflag ();
+  MPFR_ASSERTN(mpfr_cmp_q (x, y) == 0);
+  MPFR_ASSERTN(mpfr_erangeflag_p ());
+
   mpq_clear (y);
   mpfr_clear (x);
   mpfr_clear (z);