Index: Objects/floatobject.c
===================================================================
--- Objects/floatobject.c	(revision 61312)
+++ Objects/floatobject.c	(working copy)
@@ -1751,9 +1751,6 @@
 
 /*----------------------------------------------------------------------------
  * _PyFloat_{Pack,Unpack}{4,8}.  See floatobject.h.
- *
- * TODO:  On platforms that use the standard IEEE-754 single and double
- * formats natively, these routines could simply copy the bytes.
  */
 int
 _PyFloat_Pack4(double x, unsigned char *p, int le)
@@ -1833,28 +1830,31 @@
 		/* Done */
 		return 0;
 
-	  Overflow:
-		PyErr_SetString(PyExc_OverflowError,
-				"float too large to pack with f format");
-		return -1;
 	}
 	else {
 		float y = (float)x;
 		const char *s = (char*)&y;
 		int i, incr = 1;
 
+		if (Py_IS_INFINITY(y) && !Py_IS_INFINITY(x))
+			goto Overflow;
+
 		if ((float_format == ieee_little_endian_format && !le)
 		    || (float_format == ieee_big_endian_format && le)) {
 			p += 3;
 			incr = -1;
 		}
-		
+
 		for (i = 0; i < 4; i++) {
 			*p = *s++;
 			p += incr;
 		}
 		return 0;
 	}
+  Overflow:
+	PyErr_SetString(PyExc_OverflowError,
+			"float too large to pack with f format");
+	return -1;
 }
 
 int
Index: Misc/NEWS
===================================================================
--- Misc/NEWS	(revision 61312)
+++ Misc/NEWS	(working copy)
@@ -21,6 +21,10 @@
 Library
 -------
 
+- Issue #705836: struct.pack(">f", x) now raises OverflowError on all
+  platforms when x is too large to fit into an IEEE 754 float; previously
+  it only raised OverflowError on non IEEE 754 platforms.
+
 - Issue #1106316: pdb.post_mortem()'s parameter, "traceback", is now
   optional: it defaults to the traceback of the exception that is currently
   being handled (is mandatory to be in the middle of an exception, otherwise
Index: Lib/test/test_struct.py
===================================================================
--- Lib/test/test_struct.py	(revision 61312)
+++ Lib/test/test_struct.py	(working copy)
@@ -482,7 +482,7 @@
     except OverflowError:
         pass
     else:
-        TestFailed("expected OverflowError")
+        raise TestFailed("expected OverflowError")
 
 test_705836()