diff --git a/dlls/combase/string.c b/dlls/combase/string.c
index 49d76958d94..99cd5913341 100644
--- a/dlls/combase/string.c
+++ b/dlls/combase/string.c
@@ -105,6 +105,8 @@ HRESULT WINAPI WindowsCreateStringReference(LPCWSTR ptr, UINT32 len,
 
     if (out == NULL || header == NULL)
         return E_INVALIDARG;
+    if (ptr != NULL && ptr[len] != '\0')
+        return E_INVALIDARG;
     if (len == 0)
     {
         *out = NULL;
@@ -112,8 +114,6 @@ HRESULT WINAPI WindowsCreateStringReference(LPCWSTR ptr, UINT32 len,
     }
     if (ptr == NULL)
         return E_POINTER;
-    if (ptr[len] != '\0')
-        return E_INVALIDARG;
     priv->buffer = (LPWSTR)ptr;
     priv->length = len;
     priv->reference = TRUE;
diff --git a/dlls/combase/tests/string.c b/dlls/combase/tests/string.c
index 5a59b504a9d..7af5f7e12c9 100644
--- a/dlls/combase/tests/string.c
+++ b/dlls/combase/tests/string.c
@@ -124,6 +124,9 @@ static void test_create_delete(void)
      * length. According to MSDN this should be E_INVALIDARG, but it returns
      * 0x80000017 in practice. */
     ok(FAILED(pWindowsCreateStringReference(input_string, 5, &header, &str)), "Incorrect error handling\n");
+    /* If the input string is non-null, it must be null-terminated even if the
+     * length is zero. */
+    ok(FAILED(pWindowsCreateStringReference(input_string, 0, &header, &str)), "Incorrect error handling\n");
     ok(pWindowsCreateStringReference(input_string, 6, NULL, &str) == E_INVALIDARG, "Incorrect error handling\n");
     ok(pWindowsCreateStringReference(input_string, 6, &header, NULL) == E_INVALIDARG, "Incorrect error handling\n");
     ok(pWindowsCreateStringReference(NULL, 6, &header, &str) == E_POINTER, "Incorrect error handling\n");
@@ -138,9 +141,21 @@ static void test_create_delete(void)
     ok(str == NULL, "Empty string not a null string\n");
     ok(pWindowsDeleteString(str) == S_OK, "Failed to delete string\n");
 
+    ok(pWindowsCreateString(input_string, 0, &str) == S_OK, "Failed to create string\n");
+    ok(str == NULL, "Empty string not a null string\n");
+    ok(pWindowsDeleteString(str) == S_OK, "Failed to delete string\n");
+
     ok(pWindowsCreateStringReference(input_empty_string, 0, &header, &str) == S_OK, "Failed to create string\n");
     ok(str == NULL, "Empty string not a null string\n");
     ok(pWindowsDeleteString(str) == S_OK, "Failed to delete string\n");
+
+    ok(pWindowsCreateString(NULL, 0, &str) == S_OK, "Failed to create string\n");
+    ok(str == NULL, "Empty string not a null string\n");
+    ok(pWindowsDeleteString(str) == S_OK, "Failed to delete string\n");
+
+    ok(pWindowsCreateStringReference(NULL, 0, &header, &str) == S_OK, "Failed to create string\n");
+    ok(str == NULL, "Empty string not a null string\n");
+    ok(pWindowsDeleteString(str) == S_OK, "Failed to delete string\n");
 }
 
 static void test_duplicate(void)