diff --git a/Python/pymath.c b/Python/pymath.c
index 6b8def9..2749688 100644
--- a/Python/pymath.c
+++ b/Python/pymath.c
@@ -1,5 +1,18 @@
 #include "Python.h"
 
+#ifdef X87_DOUBLE_ROUNDING
+/* On x86 platforms using an x87 FPU, this function is called from the
+   Py_FORCE_DOUBLE macro (defined in pymath.h) to force a floating-point
+   number out of an 80-bit x87 FPU register and into a 64-bit memory location,
+   thus rounding from extended precision to double precision. */
+double _Py_force_double(double x)
+{
+	volatile double y;
+	y = x;
+	return y;
+}
+#endif
+
 #ifndef HAVE_HYPOT
 double hypot(double x, double y)
 {