diff --git a/src/vrend_decode.c b/src/vrend_decode.c
index ff15f35..e36e1f6 100644
--- a/src/vrend_decode.c
+++ b/src/vrend_decode.c
@@ -172,7 +172,7 @@ static int vrend_decode_set_viewport_state(struct vrend_decode_ctx *ctx, int len
 {
    struct pipe_viewport_state vps[PIPE_MAX_VIEWPORTS];
    int i, v;
-   int num_viewports, start_slot;
+   uint32_t num_viewports, start_slot;
    if (length < 1)
       return EINVAL;
 
diff --git a/src/vrend_renderer.c b/src/vrend_renderer.c
index c8e5b60..2e380a9 100644
--- a/src/vrend_renderer.c
+++ b/src/vrend_renderer.c
@@ -1562,8 +1562,8 @@ void vrend_set_framebuffer_state(struct vrend_context *ctx,
  * an FBO already so don't need to invert rendering?
  */
 void vrend_set_viewport_states(struct vrend_context *ctx,
-                               int start_slot,
-                               int num_viewports,
+                               uint32_t start_slot,
+                               uint32_t num_viewports,
                                const struct pipe_viewport_state *state)
 {
    /* convert back to glViewport */
@@ -1574,6 +1574,12 @@ void vrend_set_viewport_states(struct vrend_context *ctx,
    GLfloat abs_s1 = fabsf(state->scale[1]);
    int i, idx;
 
+   if (num_viewports > PIPE_MAX_VIEWPORTS ||
+       start_slot > (PIPE_MAX_VIEWPORTS - num_viewports)) {
+      report_context_error(ctx, VIRGL_ERROR_CTX_ILLEGAL_CMD_BUFFER, num_viewports);
+      return;
+   }
+
    for (i = 0; i < num_viewports; i++) {
       idx = start_slot + i;
 
diff --git a/src/vrend_renderer.h b/src/vrend_renderer.h
index 79fe081..78d00bd 100644
--- a/src/vrend_renderer.h
+++ b/src/vrend_renderer.h
@@ -210,7 +210,7 @@ int vrend_transfer_inline_write(struct vrend_context *ctx,
                                 unsigned usage);
 
 void vrend_set_viewport_states(struct vrend_context *ctx,
-                               int start_slot, int num_viewports,
+                               uint32_t start_slot, uint32_t num_viewports,
                                const struct pipe_viewport_state *state);
 void vrend_set_num_sampler_views(struct vrend_context *ctx,
                                  uint32_t shader_type,