Index: Objects/unicodeobject.c
===================================================================
--- Objects/unicodeobject.c	(revision 54152)
+++ Objects/unicodeobject.c	(working copy)
@@ -7276,7 +7276,8 @@
        always given), therefore increase the length by one.
 
     */
-    if ((type == 'g' && buflen <= (size_t)10 + (size_t)prec) ||
+    if (((type == 'g' || type == 'G') && 
+          buflen <= (size_t)10 + (size_t)prec) ||
 	(type == 'f' && buflen <= (size_t)53 + (size_t)prec)) {
 	PyErr_SetString(PyExc_OverflowError,
 			"formatted float is too long (precision too large?)");
Index: Objects/stringobject.c
===================================================================
--- Objects/stringobject.c	(revision 54152)
+++ Objects/stringobject.c	(working copy)
@@ -4174,7 +4174,8 @@
 	   always given), therefore increase the length by one.
 
 	*/
-	if ((type == 'g' && buflen <= (size_t)10 + (size_t)prec) ||
+	if (((type == 'g' || type == 'G') &&
+              buflen <= (size_t)10 + (size_t)prec) ||
 	    (type == 'f' && buflen <= (size_t)53 + (size_t)prec)) {
 		PyErr_SetString(PyExc_OverflowError,
 			"formatted float is too long (precision too large?)");
Index: Lib/test/test_format.py
===================================================================
--- Lib/test/test_format.py	(revision 54152)
+++ Lib/test/test_format.py	(working copy)
@@ -7,6 +7,7 @@
 # test on unicode strings as well
 
 overflowok = 1
+overflowrequired = 0
 
 def testformat(formatstr, args, output=None):
     if verbose:
@@ -23,15 +24,21 @@
         if verbose:
             print('overflow (this is fine)')
     else:
-        if output and result != output:
+        if overflowrequired:
             if verbose:
                 print('no')
+            print("overflow expected on %s %% %s" % \
+                  (repr(formatstr), repr(args)))
+        elif output and result != output:
+            if verbose:
+                print('no')
             print("%s %% %s == %s != %s" %\
-                (repr(formatstr), repr(args), repr(result), repr(output)))
+                  (repr(formatstr), repr(args), repr(result), repr(output)))
         else:
             if verbose:
                 print('yes')
 
+
 def testboth(formatstr, *args):
     testformat(formatstr, *args)
     if have_unicode:
@@ -55,6 +62,14 @@
 # test some ridiculously large precision, expect overflow
 testboth('%12.*f', (123456, 1.0))
 
+# check for internal overflow validation on length of precision
+overflowrequired = 1
+testboth("%#.*g", (110, -1.e+100/3.))
+testboth("%#.*G", (110, -1.e+100/3.))
+testboth("%#.*f", (110, -1.e+100/3.))
+testboth("%#.*F", (110, -1.e+100/3.))
+overflowrequired = 0
+
 # Formatting of long integers. Overflow is not ok
 overflowok = 0
 testboth("%x", 10, "a")