diff --git a/src/mapi/glapi/gen/gl_marshal.py b/src/mapi/glapi/gen/gl_marshal.py
index 74bd57beb32..43f70efb988 100644
--- a/src/mapi/glapi/gen/gl_marshal.py
+++ b/src/mapi/glapi/gen/gl_marshal.py
@@ -127,6 +127,8 @@ class PrintCode(gl_XML.gl_print_base):
             if p.count:
                 out('memcpy(cmd->{0}, {0}, {1});'.format(
                         p.name, p.size_string()))
+            elif p.type_string() == 'GLenum':
+                out('cmd->{0} = MIN2({0}, 0xffff); /* clamped to 0xffff (invalid enum) */'.format(p.name))
             else:
                 out('cmd->{0} = {0};'.format(p.name))
         if variable_params:
@@ -164,10 +166,10 @@ class PrintCode(gl_XML.gl_print_base):
             'GLboolean': 1,
             'GLbyte': 1,
             'GLubyte': 1,
+            'GLenum': 2, # uses GLenum16, clamped to 0xffff (invalid enum)
             'GLshort': 2,
             'GLushort': 2,
             'GLhalfNV': 2,
-            'GLenum': 4,
             'GLint': 4,
             'GLuint': 4,
             'GLbitfield': 4,
@@ -212,7 +214,10 @@ class PrintCode(gl_XML.gl_print_base):
                     out('{0} {1}[{2}];'.format(
                             p.get_base_type_string(), p.name, p.count))
                 else:
-                    out('{0} {1};'.format(p.type_string(), p.name))
+                    type = p.type_string()
+                    if type == 'GLenum':
+                        type = 'GLenum16'
+                    out('{0} {1};'.format(type, p.name))
 
             for p in variable_params:
                 if p.img_null_flag:
diff --git a/src/mesa/main/glthread.h b/src/mesa/main/glthread.h
index 6ed17a3c69d..efc579ac3e4 100644
--- a/src/mesa/main/glthread.h
+++ b/src/mesa/main/glthread.h
@@ -52,6 +52,7 @@
 #include "GL/gl.h"
 #include "compiler/shader_enums.h"
 #include "main/config.h"
+#include "glheader.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -128,7 +129,7 @@ struct glthread_client_attrib {
 struct glthread_attrib_node {
    GLbitfield Mask;
    int ActiveTexture;
-   GLenum MatrixMode;
+   GLenum16 MatrixMode;
    bool CullFace;
    bool DepthTest;
 };
@@ -157,7 +158,7 @@ struct glthread_state
    bool inside_begin_end;
 
    /** Display lists. */
-   GLenum ListMode; /**< Zero if not inside display list, else list mode. */
+   GLenum16 ListMode; /**< Zero if not inside display list, else list mode. */
    unsigned ListBase;
    unsigned ListCallDepth;
 
@@ -226,7 +227,7 @@ struct glthread_state
 
    /** Basic matrix state tracking. */
    int ActiveTexture;
-   GLenum MatrixMode;
+   GLenum16 MatrixMode;
    gl_matrix_index MatrixIndex;
    struct glthread_attrib_node AttribStack[MAX_ATTRIB_STACK_DEPTH];
    int AttribStackDepth;
diff --git a/src/mesa/main/glthread_draw.c b/src/mesa/main/glthread_draw.c
index 3af1d3d3e06..2e709c44fd2 100644
--- a/src/mesa/main/glthread_draw.c
+++ b/src/mesa/main/glthread_draw.c
@@ -568,8 +568,8 @@ sync:
 struct marshal_cmd_DrawElementsInstancedARB
 {
    struct marshal_cmd_base cmd_base;
-   GLenum mode;
-   GLenum type;
+   GLenum16 mode;
+   GLenum16 type;
    GLsizei count;
    GLsizei instance_count;
    GLint basevertex;
@@ -606,8 +606,8 @@ _mesa_unmarshal_DrawElementsInstancedARB(struct gl_context *ctx,
 struct marshal_cmd_DrawRangeElementsBaseVertex
 {
    struct marshal_cmd_base cmd_base;
-   GLenum mode;
-   GLenum type;
+   GLenum16 mode;
+   GLenum16 type;
    GLsizei count;
    GLint basevertex;
    GLuint min_index;
@@ -645,9 +645,9 @@ draw_elements_async(struct gl_context *ctx, GLenum mode, GLsizei count,
       struct marshal_cmd_DrawRangeElementsBaseVertex *cmd =
          _mesa_glthread_allocate_command(ctx, DISPATCH_CMD_DrawRangeElementsBaseVertex, cmd_size);
 
-      cmd->mode = mode;
+      cmd->mode = MIN2(mode, 0xffff);
+      cmd->type = MIN2(type, 0xffff);
       cmd->count = count;
-      cmd->type = type;
       cmd->indices = indices;
       cmd->basevertex = basevertex;
       cmd->min_index = min_index;
@@ -657,9 +657,9 @@ draw_elements_async(struct gl_context *ctx, GLenum mode, GLsizei count,
       struct marshal_cmd_DrawElementsInstancedARB *cmd =
          _mesa_glthread_allocate_command(ctx, DISPATCH_CMD_DrawElementsInstancedARB, cmd_size);
 
-      cmd->mode = mode;
+      cmd->mode = MIN2(mode, 0xffff);
+      cmd->type = MIN2(type, 0xffff);
       cmd->count = count;
-      cmd->type = type;
       cmd->indices = indices;
       cmd->instance_count = instance_count;
       cmd->basevertex = basevertex;
@@ -671,8 +671,8 @@ struct marshal_cmd_DrawElementsInstancedBaseVertexBaseInstance
 {
    struct marshal_cmd_base cmd_base;
    bool index_bounds_valid;
-   GLenum mode;
-   GLenum type;
+   GLenum16 mode;
+   GLenum16 type;
    GLsizei count;
    GLsizei instance_count;
    GLint basevertex;
@@ -756,9 +756,9 @@ draw_elements_async_user(struct gl_context *ctx, GLenum mode, GLsizei count,
    struct marshal_cmd_DrawElementsInstancedBaseVertexBaseInstance *cmd;
 
    cmd = _mesa_glthread_allocate_command(ctx, DISPATCH_CMD_DrawElementsInstancedBaseVertexBaseInstance, cmd_size);
-   cmd->mode = mode;
+   cmd->mode = MIN2(mode, 0xffff);
+   cmd->type = MIN2(type, 0xffff);
    cmd->count = count;
-   cmd->type = type;
    cmd->indices = indices;
    cmd->instance_count = instance_count;
    cmd->basevertex = basevertex;
@@ -887,8 +887,8 @@ struct marshal_cmd_MultiDrawElementsBaseVertex
 {
    struct marshal_cmd_base cmd_base;
    bool has_base_vertex;
-   GLenum mode;
-   GLenum type;
+   GLenum16 mode;
+   GLenum16 type;
    GLsizei draw_count;
    GLuint user_buffer_mask;
    struct gl_buffer_object *index_buffer;
@@ -972,8 +972,8 @@ multi_draw_elements_async(struct gl_context *ctx, GLenum mode,
    }
 
    cmd = _mesa_glthread_allocate_command(ctx, DISPATCH_CMD_MultiDrawElementsBaseVertex, cmd_size);
-   cmd->mode = mode;
-   cmd->type = type;
+   cmd->mode = MIN2(mode, 0xffff);
+   cmd->type = MIN2(type, 0xffff);
    cmd->draw_count = draw_count;
    cmd->user_buffer_mask = user_buffer_mask;
    cmd->index_buffer = index_buffer;
diff --git a/src/mesa/main/glthread_marshal.h b/src/mesa/main/glthread_marshal.h
index 9c56e57e78c..f390cb9453c 100644
--- a/src/mesa/main/glthread_marshal.h
+++ b/src/mesa/main/glthread_marshal.h
@@ -613,7 +613,7 @@ _mesa_glthread_MatrixMode(struct gl_context *ctx, GLenum mode)
       return;
 
    ctx->GLThread.MatrixIndex = _mesa_get_matrix_index(ctx, mode);
-   ctx->GLThread.MatrixMode = mode;
+   ctx->GLThread.MatrixMode = MIN2(mode, 0xffff);
 }
 
 static inline void
@@ -756,10 +756,10 @@ _mesa_glthread_CallLists(struct gl_context *ctx, GLsizei n, GLenum type,
 }
 
 static inline void
-_mesa_glthread_NewList(struct gl_context *ctx, GLuint list, GLuint mode)
+_mesa_glthread_NewList(struct gl_context *ctx, GLuint list, GLenum mode)
 {
    if (!ctx->GLThread.ListMode)
-      ctx->GLThread.ListMode = mode;
+      ctx->GLThread.ListMode = MIN2(mode, 0xffff);
 }
 
 static inline void