diff --git a/src/calibre/__init__.py b/src/calibre/__init__.py
index f105db8879..c3039794b8 100644
--- a/src/calibre/__init__.py
+++ b/src/calibre/__init__.py
@@ -543,9 +543,9 @@ def strftime(fmt, t=None):
         t[0] = replacement
     ans = None
     if iswindows:
-        if isinstance(fmt, unicode):
-            fmt = fmt.encode('mbcs', 'replace')
-        fmt = fmt.replace(b'%e', b'%#d')
+        if isinstance(fmt, bytes):
+            fmt = fmt.decode('mbcs', 'replace')
+        fmt = fmt.replace(u'%e', u'%#d')
         ans = plugins['winutil'][0].strftime(fmt, t)
     else:
         ans = time.strftime(fmt, t).decode(preferred_encoding, 'replace')
diff --git a/src/calibre/utils/windows/winutil.c b/src/calibre/utils/windows/winutil.c
index 567493bbe4..04b5e04f8c 100644
--- a/src/calibre/utils/windows/winutil.c
+++ b/src/calibre/utils/windows/winutil.c
@@ -300,84 +300,69 @@ winutil_strftime(PyObject *self, PyObject *args)
 {
     PyObject *tup = NULL;
     struct tm buf;
-    const char *_fmt;
-    size_t fmtlen, buflen;
-    wchar_t *outbuf = NULL, *fmt = NULL;
+    size_t buflen;
+    wchar_t *outbuf = NULL;
+    Py_UNICODE *fmt = NULL;
+    int fmtlen;
     size_t i;
-    memset((void *) &buf, '\0', sizeof(buf));
+    memset((void *) &buf, 0, sizeof(buf));
 
-    if (!PyArg_ParseTuple(args, "s|O:strftime", &_fmt, &tup))
-        return NULL;
-
-    if (mbstowcs_s(&fmtlen, NULL, 0, _fmt, strlen(_fmt)) != 0) {
-        PyErr_SetString(PyExc_ValueError, "Failed to convert fmt to wchar");
-        return NULL;
-    }
-    fmt = (wchar_t *)PyMem_Malloc((fmtlen+2)*sizeof(wchar_t));
-    if (fmt == NULL) return PyErr_NoMemory();
-    if (mbstowcs_s(&fmtlen, fmt, fmtlen+2, _fmt, strlen(_fmt)) != 0) {
-        PyErr_SetString(PyExc_ValueError, "Failed to convert fmt to wchar");
-        goto end;
-    }
+    if (!PyArg_ParseTuple(args, "u#|O:strftime", &fmt, &fmtlen, &tup)) return NULL;
 
     if (tup == NULL) {
         time_t tt = time(NULL);
         if(localtime_s(&buf, &tt) != 0) {
             PyErr_SetString(PyExc_ValueError, "Failed to get localtime()");
-            goto end;
+            return NULL;
         }
-    } else if (!gettmarg(tup, &buf))
-        goto end;
+    } else if (!gettmarg(tup, &buf)) return NULL;
 
-    if (buf.tm_mon == -1)
-        buf.tm_mon = 0;
+    if (buf.tm_mon == -1) buf.tm_mon = 0;
     else if (buf.tm_mon < 0 || buf.tm_mon > 11) {
-            PyErr_SetString(PyExc_ValueError, "month out of range");
-            goto end;
-        }
-    if (buf.tm_mday == 0)
-        buf.tm_mday = 1;
+        PyErr_SetString(PyExc_ValueError, "month out of range");
+        return NULL;
+    }
+    if (buf.tm_mday == 0) buf.tm_mday = 1;
     else if (buf.tm_mday < 0 || buf.tm_mday > 31) {
-            PyErr_SetString(PyExc_ValueError, "day of month out of range");
-            goto end;
-        }
-        if (buf.tm_hour < 0 || buf.tm_hour > 23) {
-            PyErr_SetString(PyExc_ValueError, "hour out of range");
-            goto end;
-        }
-        if (buf.tm_min < 0 || buf.tm_min > 59) {
-            PyErr_SetString(PyExc_ValueError, "minute out of range");
-            goto end;
-        }
-        if (buf.tm_sec < 0 || buf.tm_sec > 61) {
-            PyErr_SetString(PyExc_ValueError, "seconds out of range");
-            goto end;
-        }
-        /* tm_wday does not need checking of its upper-bound since taking
-        ``% 7`` in gettmarg() automatically restricts the range. */
-        if (buf.tm_wday < 0) {
-            PyErr_SetString(PyExc_ValueError, "day of week out of range");
-            goto end;
-        }
-    if (buf.tm_yday == -1)
-        buf.tm_yday = 0;
+        PyErr_SetString(PyExc_ValueError, "day of month out of range");
+        return NULL;
+    }
+    if (buf.tm_hour < 0 || buf.tm_hour > 23) {
+        PyErr_SetString(PyExc_ValueError, "hour out of range");
+        return NULL;
+    }
+    if (buf.tm_min < 0 || buf.tm_min > 59) {
+        PyErr_SetString(PyExc_ValueError, "minute out of range");
+        return NULL;
+    }
+    if (buf.tm_sec < 0 || buf.tm_sec > 61) {
+        PyErr_SetString(PyExc_ValueError, "seconds out of range");
+        return NULL;
+    }
+    /* tm_wday does not need checking of its upper-bound since taking
+       ``% 7`` in gettmarg() automatically restricts the range. */
+    if (buf.tm_wday < 0) {
+        PyErr_SetString(PyExc_ValueError, "day of week out of range");
+        return NULL;
+    }
+    if (buf.tm_yday == -1) buf.tm_yday = 0;
     else if (buf.tm_yday < 0 || buf.tm_yday > 365) {
-            PyErr_SetString(PyExc_ValueError, "day of year out of range");
-            goto end;
-        }
-        if (buf.tm_isdst < -1 || buf.tm_isdst > 1) {
-            PyErr_SetString(PyExc_ValueError,
-                            "daylight savings flag out of range");
-            goto end;
-        }
+        PyErr_SetString(PyExc_ValueError, "day of year out of range");
+        return NULL;
+    }
+    if (buf.tm_isdst < -1 || buf.tm_isdst > 1) {
+        PyErr_SetString(PyExc_ValueError,
+                "daylight savings flag out of range");
+        return NULL;
+    }
 
-    for (i = 5*fmtlen; ; i += i) {
+    for (i = 5*(unsigned int)fmtlen; ; i += i) {
         outbuf = (wchar_t *)PyMem_Malloc(i*sizeof(wchar_t));
         if (outbuf == NULL) {
-            PyErr_NoMemory(); goto end;
+            PyErr_NoMemory(); return NULL;
         }
         buflen = wcsftime(outbuf, i, fmt, &buf);
-        if (buflen > 0 || i >= 256 * fmtlen) {
+        if (buflen > 0 || i >= 256 * (unsigned int)fmtlen) {
             /* If the buffer is 256 times as long as the format,
                it's probably not failing for lack of room!
                More likely, the format yields an empty result,
@@ -385,20 +370,17 @@ winutil_strftime(PyObject *self, PyObject *args)
                is unknown. */
             PyObject *ret;
             ret = PyUnicode_FromWideChar(outbuf, buflen);
-            PyMem_Free(outbuf); PyMem_Free(fmt);
+            PyMem_Free(outbuf);
             return ret;
         }
         PyMem_Free(outbuf);
-#if defined _MSC_VER && _MSC_VER >= 1400 && defined(__STDC_SECURE_LIB__)
         /* VisualStudio .NET 2005 does this properly */
         if (buflen == 0 && errno == EINVAL) {
             PyErr_SetString(PyExc_ValueError, "Invalid format string");
-            goto end;
+            return NULL;
         }
-#endif
     }
-end:
-    PyMem_Free(fmt); return NULL;
+    return NULL;
 }