diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 58606aa46112f83dd9d7aa41a9d4728219d4871a..204b3911cc48fbee0742214eaa227eabffbb53ba 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -2205,8 +2205,8 @@ zero_to_inf_range (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, int signbit_known)
    [1., 1.] = op1 + [1., 1.].  op1's range is not [0., 0.], but
    [-0x1.0p-54, 0x1.0p-53] (when not -frounding-math), any value for
    which adding 1. to it results in 1. after rounding to nearest.
-   So, for op1_range/op2_range extend the lhs range by 1ulp in each
-   direction.  See PR109008 for more details.  */
+   So, for op1_range/op2_range extend the lhs range by 1ulp (or 0.5ulp)
+   in each direction.  See PR109008 for more details.  */
 
 static frange
 float_widen_lhs_range (tree type, const frange &lhs)
@@ -2230,6 +2230,14 @@ float_widen_lhs_range (tree type, const frange &lhs)
 	  lb = dconstm1;
 	  SET_REAL_EXP (&lb, FLOAT_MODE_FORMAT (TYPE_MODE (type))->emax + 1);
 	}
+      if (!flag_rounding_math && !MODE_COMPOSITE_P (TYPE_MODE (type)))
+	{
+	  /* If not -frounding-math nor IBM double double, actually widen
+	     just by 0.5ulp rather than 1ulp.  */
+	  REAL_VALUE_TYPE tem;
+	  real_arithmetic (&tem, PLUS_EXPR, &lhs.lower_bound (), &lb);
+	  real_arithmetic (&lb, RDIV_EXPR, &tem, &dconst2);
+	}
     }
   if (real_isfinite (&ub))
     {
@@ -2240,6 +2248,14 @@ float_widen_lhs_range (tree type, const frange &lhs)
 	  ub = dconst1;
 	  SET_REAL_EXP (&ub, FLOAT_MODE_FORMAT (TYPE_MODE (type))->emax + 1);
 	}
+      if (!flag_rounding_math && !MODE_COMPOSITE_P (TYPE_MODE (type)))
+	{
+	  /* If not -frounding-math nor IBM double double, actually widen
+	     just by 0.5ulp rather than 1ulp.  */
+	  REAL_VALUE_TYPE tem;
+	  real_arithmetic (&tem, PLUS_EXPR, &lhs.upper_bound (), &ub);
+	  real_arithmetic (&ub, RDIV_EXPR, &tem, &dconst2);
+	}
     }
   /* Temporarily disable -ffinite-math-only, so that frange::set doesn't
      reduce the range back to real_min_representable (type) as lower bound