diff --git a/dlls/msvcirt/msvcirt.c b/dlls/msvcirt/msvcirt.c
index 3adaf7425c9..07aea3ee256 100644
--- a/dlls/msvcirt/msvcirt.c
+++ b/dlls/msvcirt/msvcirt.c
@@ -1126,8 +1126,8 @@ int __thiscall filebuf_sync(filebuf *this)
         count = this->base.pptr - this->base.pbase;
         if (count > 0 && _write(this->fd, this->base.pbase, count) != count)
             return EOF;
-        this->base.pbase = this->base.pptr = this->base.epptr = NULL;
     }
+    this->base.pbase = this->base.pptr = this->base.epptr = NULL;
     /* flush input buffer */
     if (this->base.egptr != NULL) {
         offset = this->base.egptr - this->base.gptr;
@@ -1143,8 +1143,8 @@ int __thiscall filebuf_sync(filebuf *this)
             if (_lseek(this->fd, -offset, SEEK_CUR) < 0)
                 return EOF;
         }
-        this->base.eback = this->base.gptr = this->base.egptr = NULL;
     }
+    this->base.eback = this->base.gptr = this->base.egptr = NULL;
     return 0;
 }
 
diff --git a/dlls/msvcirt/tests/msvcirt.c b/dlls/msvcirt/tests/msvcirt.c
index 3e8b548b5b7..13b83972131 100644
--- a/dlls/msvcirt/tests/msvcirt.c
+++ b/dlls/msvcirt/tests/msvcirt.c
@@ -1419,6 +1419,46 @@ static void test_filebuf(void)
     ok(fb1.base.gptr == NULL, "wrong get pointer, expected %p got %p\n", NULL, fb1.base.gptr);
     ok(fb1.base.pptr == NULL, "wrong put pointer, expected %p got %p\n", NULL, fb1.base.pptr);
     ok(_tell(fb1.fd) == 0, "_tell failed\n");
+    fb1.base.pbase = fb1.base.pptr = fb1.base.base;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.pbase == NULL, "wrong put base, expected %p got %p\n", NULL, fb1.base.pbase);
+    ok(fb1.base.pptr == NULL, "wrong put pointer, expected %p got %p\n", NULL, fb1.base.pptr);
+    fb1.base.epptr = fb1.base.ebuf;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.epptr == NULL, "wrong put end, expected %p got %p\n", NULL, fb1.base.epptr);
+    fb1.base.pbase = fb1.base.base;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.pbase == NULL, "wrong put base, expected %p got %p\n", NULL, fb1.base.pbase);
+    fb1.base.pbase = fb1.base.base;
+    fb1.base.epptr = fb1.base.ebuf;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.pbase == NULL, "wrong put base, expected %p got %p\n", NULL, fb1.base.pbase);
+    ok(fb1.base.epptr == NULL, "wrong put end, expected %p got %p\n", NULL, fb1.base.epptr);
+    fb1.base.eback = fb1.base.base;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.eback == NULL, "wrong get base, expected %p got %p\n", NULL, fb1.base.eback);
+    fb1.base.eback = fb1.base.gptr = fb1.base.base;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.gptr == NULL, "wrong get base, expected %p got %p\n", NULL, fb1.base.gptr);
+    fb1.base.gptr = fb1.base.base;
+    fb1.base.egptr = fb1.base.base + 100;
+    fb1.base.pbase = fb1.base.base;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == -1, "wrong return, expected -1 got %d\n", ret);
+    ok(fb1.base.gptr == fb1.base.base, "wrong get base, expected %p got %p\n", fb1.base.base, fb1.base.gptr);
+    ok(fb1.base.egptr == fb1.base.base + 100, "wrong get base, expected %p got %p\n", fb1.base.base + 100, fb1.base.egptr);
+    ok(fb1.base.pbase == NULL, "wrong put base, expected %p got %p\n", NULL, fb1.base.pbase);
+    fb1.base.egptr = NULL;
+    ret = (int) call_func1(p_filebuf_sync, &fb1);
+    ok(ret == 0, "wrong return, expected 0 got %d\n", ret);
+    ok(fb1.base.gptr == NULL, "wrong get base, expected %p got %p\n", NULL, fb1.base.gptr);
+    ok(fb1.base.egptr == NULL, "wrong get base, expected %p got %p\n", NULL, fb1.base.egptr);
     ret = (int) call_func1(p_filebuf_sync, &fb2);
     ok(ret == -1, "wrong return, expected -1 got %d\n", ret);
     fb3.base.eback = fb3.base.base;