diff --git a/Include/pyerrors.h b/Include/pyerrors.h
index 3c57e2f0314..bfc36ae03ac 100644
--- a/Include/pyerrors.h
+++ b/Include/pyerrors.h
@@ -106,6 +106,22 @@ extern DL_IMPORT(void) PyErr_SetInterrupt(void);
 extern DL_IMPORT(void) PyErr_SyntaxLocation(char *, int);
 extern DL_IMPORT(PyObject *) PyErr_ProgramText(char *, int);
 	
+/* These APIs aren't really part of the error implementation, but
+   often needed to format error messages; the native C lib APIs are
+   not available on all platforms, which is why we provide emulations
+   for those platforms in Python/mysnprintf.c */
+#if defined(MS_WIN32) && !defined(HAVE_SNPRINTF)
+# define HAVE_SNPRINTF
+# define snprintf _snprintf
+# define vsnprintf _vsnprintf
+#endif
+#ifndef HAVE_SNPRINTF
+extern DL_IMPORT(int) PyOS_snprintf(char *str, size_t size, const char  *format, ...);
+extern DL_IMPORT(int) PyOS_vsnprintf(char *str, size_t size, const char  *format, va_list va);
+#else
+# define PyOS_vsnprintf	vsnprintf
+# define PyOS_snprintf	snprintf
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 3ca3397abd9..9fbf29d8f0c 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -214,6 +214,7 @@ PYTHON_OBJS=	\
 		Python/marshal.o \
 		Python/modsupport.o \
 		Python/mystrtoul.o \
+		Python/mysnprintf.o \
 		Python/pyfpe.o \
 		Python/pystate.o \
 		Python/pythonrun.o \
diff --git a/Python/modsupport.c b/Python/modsupport.c
index 08685898da2..eb0818cc95c 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -26,8 +26,8 @@ char *_Py_PackageContext = NULL;
 */
 
 static char api_version_warning[] =
-"WARNING: Python C API version mismatch for module %s:\n\
-  This Python has API version %d, module %s has version %d.\n";
+"Python C API version mismatch for module %.100s:\
+ This Python has API version %d, module %.100s has version %d.";
 
 PyObject *
 Py_InitModule4(char *name, PyMethodDef *methods, char *doc,
@@ -37,9 +37,15 @@ Py_InitModule4(char *name, PyMethodDef *methods, char *doc,
 	PyMethodDef *ml;
 	if (!Py_IsInitialized())
 	    Py_FatalError("Interpreter not initialized (version mismatch?)");
-	if (module_api_version != PYTHON_API_VERSION)
-		fprintf(stderr, api_version_warning,
-			name, PYTHON_API_VERSION, name, module_api_version);
+	if (module_api_version != PYTHON_API_VERSION) {
+		char message[512];
+		PyOS_snprintf(message, sizeof(message), 
+			      api_version_warning, name, 
+			      PYTHON_API_VERSION, name, 
+			      module_api_version);
+		if (PyErr_Warn(PyExc_RuntimeWarning, message)) 
+			return NULL;
+	}
 	if (_Py_PackageContext != NULL) {
 		char *p = strrchr(_Py_PackageContext, '.');
 		if (p != NULL && strcmp(name, p+1) == 0) {
diff --git a/Python/mysnprintf.c b/Python/mysnprintf.c
new file mode 100644
index 00000000000..e6c3fcedc66
--- /dev/null
+++ b/Python/mysnprintf.c
@@ -0,0 +1,96 @@
+
+#include "Python.h"
+
+/* snprintf() emulation for platforms which don't have it (yet). 
+   
+   Return value
+
+       The number of characters printed (not including the trailing
+       `\0' used to end output to strings) or a negative number in
+       case of an error.
+
+       PyOS_snprintf and PyOS_vsnprintf do not write more than size
+       bytes (including the trailing '\0').
+
+       If the output would have been truncated, they return the number
+       of characters (excluding the trailing '\0') which would have
+       been written to the final string if enough space had been
+       available. This is inline with the C99 standard.
+
+*/
+
+#include <ctype.h>
+
+#ifndef HAVE_SNPRINTF
+
+static
+int myvsnprintf(char *str, size_t size, const char  *format, va_list va)
+{
+    char *buffer = PyMem_Malloc(size + 512);
+    int len;
+    
+    if (buffer == NULL)
+	return -1;
+    len = vsprintf(buffer, format, va);
+    if (len < 0) {
+	PyMem_Free(buffer);
+	return len;
+    }
+    len++;
+    if (len > size + 512)
+	Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf");
+    if (len > size) {
+	PyMem_Free(buffer);
+	return len - 1;
+    }
+    memcpy(str, buffer, len);
+    PyMem_Free(buffer);
+    return len - 1;
+}
+
+int PyOS_snprintf(char *str, size_t size, const  char  *format, ...)
+{
+    int rc;
+    va_list va;
+
+    va_start(va, format);
+    rc = myvsnprintf(str, size, format, va);
+    va_end(va);
+    return rc;
+}
+
+int PyOS_vsnprintf(char *str, size_t size, const char  *format, va_list va)
+{
+    return myvsnprintf(str, size, format, va);
+}
+
+#else
+
+/* Make sure that a C API is included in the lib */
+
+#ifdef PyOS_snprintf
+# undef PyOS_snprintf
+#endif
+
+int PyOS_snprintf(char *str, size_t size, const  char  *format, ...)
+{
+    int rc;
+    va_list va;
+
+    va_start(va, format);
+    rc = vsnprintf(str, size, format, va);
+    va_end(va);
+    return rc;
+}
+
+#ifdef PyOS_vsnprintf
+# undef PyOS_vsnprintf
+#endif
+
+int PyOS_vsnprintf(char *str, size_t size, const char  *format, va_list va)
+{
+    return vsnprintf(str, size, format, va);
+}
+
+#endif
+