diff --git a/src/glsl/nir/spirv_to_nir.c b/src/glsl/nir/spirv_to_nir.c
index c8594085d5e..973ff7c6777 100644
--- a/src/glsl/nir/spirv_to_nir.c
+++ b/src/glsl/nir/spirv_to_nir.c
@@ -633,21 +633,44 @@ vtn_handle_constant(struct vtn_builder *b, SpvOp opcode,
 }
 
 static void
-vtn_get_builtin_location(SpvBuiltIn builtin, int *location,
+set_mode_system_value(nir_variable_mode *mode)
+{
+   assert(*mode == nir_var_system_value || *mode == nir_var_shader_in);
+   *mode = nir_var_system_value;
+}
+
+static void
+validate_per_vertex_mode(struct vtn_builder *b, nir_variable_mode mode)
+{
+   switch (b->shader->stage) {
+   case MESA_SHADER_VERTEX:
+      assert(mode == nir_var_shader_out);
+      break;
+   case MESA_SHADER_GEOMETRY:
+      assert(mode == nir_var_shader_out || mode == nir_var_shader_in);
+      break;
+   default:
+      assert(!"Invalid shader stage");
+   }
+}
+
+static void
+vtn_get_builtin_location(struct vtn_builder *b,
+                         SpvBuiltIn builtin, int *location,
                          nir_variable_mode *mode)
 {
    switch (builtin) {
    case SpvBuiltInPosition:
       *location = VARYING_SLOT_POS;
-      *mode = nir_var_shader_out;
+      validate_per_vertex_mode(b, *mode);
       break;
    case SpvBuiltInPointSize:
       *location = VARYING_SLOT_PSIZ;
-      *mode = nir_var_shader_out;
+      validate_per_vertex_mode(b, *mode);
       break;
    case SpvBuiltInClipDistance:
       *location = VARYING_SLOT_CLIP_DIST0; /* XXX CLIP_DIST1? */
-      *mode = nir_var_shader_in;
+      validate_per_vertex_mode(b, *mode);
       break;
    case SpvBuiltInCullDistance:
       /* XXX figure this out */
@@ -657,11 +680,11 @@ vtn_get_builtin_location(SpvBuiltIn builtin, int *location,
        * builtin keyword VertexIndex to indicate the non-zero-based value.
        */
       *location = SYSTEM_VALUE_VERTEX_ID_ZERO_BASE;
-      *mode = nir_var_system_value;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInInstanceId:
       *location = SYSTEM_VALUE_INSTANCE_ID;
-      *mode = nir_var_system_value;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInPrimitiveId:
       *location = VARYING_SLOT_PRIMITIVE_ID;
@@ -669,7 +692,7 @@ vtn_get_builtin_location(SpvBuiltIn builtin, int *location,
       break;
    case SpvBuiltInInvocationId:
       *location = SYSTEM_VALUE_INVOCATION_ID;
-      *mode = nir_var_system_value;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInLayer:
       *location = VARYING_SLOT_LAYER;
@@ -682,35 +705,40 @@ vtn_get_builtin_location(SpvBuiltIn builtin, int *location,
       unreachable("no tessellation support");
    case SpvBuiltInFragCoord:
       *location = VARYING_SLOT_POS;
-      *mode = nir_var_shader_in;
+      assert(b->shader->stage == MESA_SHADER_FRAGMENT);
+      assert(*mode == nir_var_shader_in);
       break;
    case SpvBuiltInPointCoord:
       *location = VARYING_SLOT_PNTC;
-      *mode = nir_var_shader_out;
+      assert(b->shader->stage == MESA_SHADER_FRAGMENT);
+      assert(*mode == nir_var_shader_in);
       break;
    case SpvBuiltInFrontFacing:
       *location = VARYING_SLOT_FACE;
-      *mode = nir_var_shader_out;
+      assert(b->shader->stage == MESA_SHADER_FRAGMENT);
+      assert(*mode == nir_var_shader_in);
       break;
    case SpvBuiltInSampleId:
       *location = SYSTEM_VALUE_SAMPLE_ID;
-      *mode = nir_var_shader_in;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInSamplePosition:
       *location = SYSTEM_VALUE_SAMPLE_POS;
-      *mode = nir_var_shader_in;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInSampleMask:
       *location = SYSTEM_VALUE_SAMPLE_MASK_IN; /* XXX out? */
-      *mode = nir_var_shader_in;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInFragColor:
       *location = FRAG_RESULT_COLOR;
-      *mode = nir_var_shader_out;
+      assert(b->shader->stage == MESA_SHADER_FRAGMENT);
+      assert(*mode == nir_var_shader_out);
       break;
    case SpvBuiltInFragDepth:
       *location = FRAG_RESULT_DEPTH;
-      *mode = nir_var_shader_out;
+      assert(b->shader->stage == MESA_SHADER_FRAGMENT);
+      assert(*mode == nir_var_shader_out);
       break;
    case SpvBuiltInNumWorkgroups:
    case SpvBuiltInWorkgroupSize:
@@ -723,11 +751,11 @@ vtn_get_builtin_location(SpvBuiltIn builtin, int *location,
       unreachable("unsupported builtin");
    case SpvBuiltInWorkgroupId:
       *location = SYSTEM_VALUE_WORK_GROUP_ID;
-      *mode = nir_var_system_value;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInLocalInvocationId:
       *location = SYSTEM_VALUE_LOCAL_INVOCATION_ID;
-      *mode = nir_var_system_value;
+      set_mode_system_value(mode);
       break;
    case SpvBuiltInHelperInvocation:
    default:
@@ -792,8 +820,8 @@ var_decoration_cb(struct vtn_builder *b, struct vtn_value *val, int member,
    case SpvDecorationBuiltIn: {
       SpvBuiltIn builtin = dec->literals[0];
 
-      nir_variable_mode mode;
-      vtn_get_builtin_location(builtin, &var->data.location, &mode);
+      nir_variable_mode mode = var->data.mode;
+      vtn_get_builtin_location(b, builtin, &var->data.location, &mode);
       var->data.explicit_location = true;
       var->data.mode = mode;
       if (mode == nir_var_shader_in || mode == nir_var_system_value)
@@ -842,7 +870,7 @@ get_builtin_variable(struct vtn_builder *b,
 
    if (!var) {
       int location;
-      vtn_get_builtin_location(builtin, &location, &mode);
+      vtn_get_builtin_location(b, builtin, &location, &mode);
 
       var = nir_variable_create(b->shader, mode, type, "builtin");