diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 1ea87b95a52..a8e235c9f9b 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,9 @@
+2018-09-26  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/87390
+	* c-typeck.c (build_binary_op): Use excess precision for
+	comparisons of integers and floating-point for C11 and later.
+
 2018-09-26  Martin Jambor  <mjambor@suse.cz>
 
 	PR c/87347
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index a5a7da0084c..9d09b8d65fd 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -11249,6 +11249,20 @@ build_binary_op (location_t location, enum tree_code code,
     case EXACT_DIV_EXPR:
       may_need_excess_precision = true;
       break;
+
+    case EQ_EXPR:
+    case NE_EXPR:
+    case LE_EXPR:
+    case GE_EXPR:
+    case LT_EXPR:
+    case GT_EXPR:
+      /* Excess precision for implicit conversions of integers to
+	 floating point in C11 and later.  */
+      may_need_excess_precision = (flag_isoc11
+				   && (ANY_INTEGRAL_TYPE_P (type0)
+				       || ANY_INTEGRAL_TYPE_P (type1)));
+      break;
+
     default:
       may_need_excess_precision = false;
       break;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index aa005e71441..16407e5244c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-09-26  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/87390
+	* gcc.target/i386/excess-precision-9.c,
+	gcc.target/i386/excess-precision-10.c: New tests.
+
 2018-09-26  Richard Biener  <rguenther@suse.de>
 
 	PR debug/87443
diff --git a/gcc/testsuite/gcc.target/i386/excess-precision-10.c b/gcc/testsuite/gcc.target/i386/excess-precision-10.c
new file mode 100644
index 00000000000..f1b9b7e1980
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/excess-precision-10.c
@@ -0,0 +1,52 @@
+/* Excess precision tests.  Test implicit conversions in comparisons:
+   excess precision in C11 mode.  */
+/* { dg-do run } */
+/* { dg-options "-std=c11 -mfpmath=387 -fexcess-precision=standard" } */
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  float f = 0x1p63f;
+  unsigned long long int u = (1ULL << 63) + 1;
+
+  if ((f == u) != 0)
+    abort ();
+
+  if ((u == f) != 0)
+    abort ();
+
+  if ((f != u) != 1)
+    abort ();
+
+  if ((u != f) != 1)
+    abort ();
+
+  if ((f < u) != 1)
+    abort ();
+
+  if ((u < f) != 0)
+    abort ();
+
+  if ((f <= u) != 1)
+    abort ();
+
+  if ((u <= f) != 0)
+    abort ();
+
+  if ((f > u) != 0)
+    abort ();
+
+  if ((u > f) != 1)
+    abort ();
+
+  if ((f >= u) != 0)
+    abort ();
+
+  if ((u >= f) != 1)
+    abort ();
+
+  exit (0);
+}
diff --git a/gcc/testsuite/gcc.target/i386/excess-precision-9.c b/gcc/testsuite/gcc.target/i386/excess-precision-9.c
new file mode 100644
index 00000000000..61e5fc104ad
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/excess-precision-9.c
@@ -0,0 +1,52 @@
+/* Excess precision tests.  Test implicit conversions in comparisons:
+   no excess precision in C99 mode.  */
+/* { dg-do run } */
+/* { dg-options "-std=c99 -mfpmath=387 -fexcess-precision=standard" } */
+
+extern void abort (void);
+extern void exit (int);
+
+int
+main (void)
+{
+  float f = 0x1p63f;
+  unsigned long long int u = (1ULL << 63) + 1;
+
+  if ((f == u) != 1)
+    abort ();
+
+  if ((u == f) != 1)
+    abort ();
+
+  if ((f != u) != 0)
+    abort ();
+
+  if ((u != f) != 0)
+    abort ();
+
+  if ((f < u) != 0)
+    abort ();
+
+  if ((u < f) != 0)
+    abort ();
+
+  if ((f <= u) != 1)
+    abort ();
+
+  if ((u <= f) != 1)
+    abort ();
+
+  if ((f > u) != 0)
+    abort ();
+
+  if ((u > f) != 0)
+    abort ();
+
+  if ((f >= u) != 1)
+    abort ();
+
+  if ((u >= f) != 1)
+    abort ();
+
+  exit (0);
+}