diff --git a/backends/vulkan/runtime/gen_vulkan_spv.py b/backends/vulkan/runtime/gen_vulkan_spv.py
index dab33fb3097..192bfa3f900 100644
--- a/backends/vulkan/runtime/gen_vulkan_spv.py
+++ b/backends/vulkan/runtime/gen_vulkan_spv.py
@@ -857,6 +857,13 @@ def create_shader_params(
         for key, value in variant_params.items():
             shader_params[key] = value
 
+        # Downgrade PRECISION to mediump for half-precision variants.
+        if (
+            shader_params.get("DTYPE") == "half"
+            and shader_params.get("PRECISION") == "highp"
+        ):
+            shader_params["PRECISION"] = "mediump"
+
         return shader_params
 
     def constructOutputMap(self) -> None: