diff --git a/Include/pyport.h b/Include/pyport.h
index be6c51fc5aa..16ee0112726 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -126,10 +126,10 @@ typedef Py_intptr_t	Py_ssize_t;
  * Py_ssize_t on the platform.
  */
 #ifndef PY_FORMAT_SIZE_T
-#   if SIZEOF_SIZE_T == SIZEOF_INT
-#       define PY_FORMAT_SIZE_T ""
-#   elif SIZEOF_SIZE_T == SIZEOF_LONG
+#   if SIZEOF_SIZE_T == SIZEOF_LONG
 #       define PY_FORMAT_SIZE_T "l"
+#   elif SIZEOF_SIZE_T == SIZEOF_INT
+#       define PY_FORMAT_SIZE_T ""
 #   elif defined(MS_WINDOWS)
 #       define PY_FORMAT_SIZE_T "I"
 #   else
diff --git a/Misc/NEWS b/Misc/NEWS
index f0d78da2123..e93a80e0cdd 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,8 @@ What's New in Python 2.6 alpha 1?
 Core and builtins
 -----------------
 
+- Fix %zd string formatting on Mac OS X so it prints negative numbers.
+
 - Allow exception instances to be directly sliced again.
 
 - Bug #1551432: Exceptions do not define an explicit __unicode__ method.  This
diff --git a/configure b/configure
index b96349a4f59..ecbdf26346b 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 51173 .
+# From configure.in Revision: 51727 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.59 for python 2.6.
 #
@@ -22110,12 +22110,26 @@ cat >>conftest.$ac_ext <<_ACEOF
 
 int main()
 {
-    char buffer[4];
+    char buffer[256];
+
+#ifdef HAVE_SSIZE_T
+typedef ssize_t Py_ssize_t;
+#elif SIZEOF_VOID_P == SIZEOF_LONG
+typedef long Py_ssize_t;
+#else
+typedef int Py_ssize_t;
+#endif
 
     if(sprintf(buffer, "%zd", (size_t)123) < 0)
        	return 1;
 
-    if (strncmp(buffer, "123", 3))
+    if (strcmp(buffer, "123"))
+	return 1;
+
+    if (sprintf(buffer, "%zd", (Py_ssize_t)-123) < 0)
+       	return 1;
+
+    if (strcmp(buffer, "-123"))
 	return 1;
 
     return 0;
diff --git a/configure.in b/configure.in
index cff71941b51..3a27294faa4 100644
--- a/configure.in
+++ b/configure.in
@@ -3352,14 +3352,28 @@ AC_TRY_RUN([#include <stdio.h>
 
 int main()
 {
-    char buffer[4];
+    char buffer[256];
+
+#ifdef HAVE_SSIZE_T
+typedef ssize_t Py_ssize_t;
+#elif SIZEOF_VOID_P == SIZEOF_LONG
+typedef long Py_ssize_t;
+#else
+typedef int Py_ssize_t;
+#endif
 
     if(sprintf(buffer, "%zd", (size_t)123) < 0)
        	return 1;
 
-    if (strncmp(buffer, "123", 3))
+    if (strcmp(buffer, "123"))
 	return 1;
-    
+
+    if (sprintf(buffer, "%zd", (Py_ssize_t)-123) < 0)
+       	return 1;
+
+    if (strcmp(buffer, "-123"))
+	return 1;
+
     return 0;
 }],
 [AC_MSG_RESULT(yes)