diff --git a/dlls/wininet/internet.c b/dlls/wininet/internet.c
index 619674ef3be..bad49e4a946 100644
--- a/dlls/wininet/internet.c
+++ b/dlls/wininet/internet.c
@@ -526,17 +526,36 @@ static DWORD APPINFO_QueryOption(object_header_t *hdr, DWORD option, void *buffe
         bufsize = *size;
 
         if (unicode) {
-            *size = (strlenW(ai->lpszAgent) + 1) * sizeof(WCHAR);
+            DWORD len = ai->lpszAgent ? strlenW(ai->lpszAgent) : 0;
+
+            *size = (len + 1) * sizeof(WCHAR);
             if(!buffer || bufsize < *size)
                 return ERROR_INSUFFICIENT_BUFFER;
 
-            strcpyW(buffer, ai->lpszAgent);
+            if (ai->lpszAgent)
+                strcpyW(buffer, ai->lpszAgent);
+            else
+                *(WCHAR *)buffer = 0;
+            /* If the buffer is copied, the returned length doesn't include
+             * the NULL terminator.
+             */
+            *size = len * sizeof(WCHAR);
         }else {
-            *size = WideCharToMultiByte(CP_ACP, 0, ai->lpszAgent, -1, NULL, 0, NULL, NULL);
+            if (ai->lpszAgent)
+                *size = WideCharToMultiByte(CP_ACP, 0, ai->lpszAgent, -1, NULL, 0, NULL, NULL);
+            else
+                *size = 1;
             if(!buffer || bufsize < *size)
                 return ERROR_INSUFFICIENT_BUFFER;
 
-            WideCharToMultiByte(CP_ACP, 0, ai->lpszAgent, -1, buffer, *size, NULL, NULL);
+            if (ai->lpszAgent)
+                WideCharToMultiByte(CP_ACP, 0, ai->lpszAgent, -1, buffer, *size, NULL, NULL);
+            else
+                *(char *)buffer = 0;
+            /* If the buffer is copied, the returned length doesn't include
+             * the NULL terminator.
+             */
+            *size -= 1;
         }
 
         return ERROR_SUCCESS;
diff --git a/dlls/wininet/tests/internet.c b/dlls/wininet/tests/internet.c
index 144c6308961..622711a21e7 100644
--- a/dlls/wininet/tests/internet.c
+++ b/dlls/wininet/tests/internet.c
@@ -184,7 +184,7 @@ static void test_InternetQueryOptionA(void)
   if (retval)
   {
       ok(!strcmp(useragent,buffer),"Got wrong user agent string %s instead of %s\n",buffer,useragent);
-      todo_wine ok(len == strlen(useragent),"Got wrong user agent length %d instead of %d\n",len,lstrlenA(useragent));
+      ok(len == strlen(useragent),"Got wrong user agent length %d instead of %d\n",len,lstrlenA(useragent));
   }
   ok(err == 0xdeadbeef, "Got wrong error code %d\n",err);
   HeapFree(GetProcessHeap(),0,buffer);
@@ -231,7 +231,7 @@ static void test_InternetQueryOptionA(void)
   len=0;
   retval=InternetQueryOptionA(hinet,INTERNET_OPTION_USER_AGENT,NULL,&len);
   err=GetLastError();
-  todo_wine ok(len == 1,"Got wrong user agent length %d instead of %d\n",len,1);
+  ok(len == 1,"Got wrong user agent length %d instead of %d\n",len,1);
   ok(retval == 0,"Got wrong return value %d\n",retval);
   ok(err == ERROR_INSUFFICIENT_BUFFER, "Got wrong error code%d\n",err);