diff --git a/app/modules/spi.c b/app/modules/spi.c
index 6074ec82..c7453e7d 100644
--- a/app/modules/spi.c
+++ b/app/modules/spi.c
@@ -33,6 +33,10 @@ static int spi_setup( lua_State *L )
   if (cpol != PLATFORM_SPI_CPOL_LOW && cpol != PLATFORM_SPI_CPOL_HIGH) {
     return luaL_error( L, "wrong arg type" );
   }
+  // CPOL_HIGH is not implemented, see app/driver/spi.c spi_master_init()
+  if (cpol == PLATFORM_SPI_CPOL_HIGH) {
+    return luaL_error( L, "cpol=high is not implemented" );
+  }
 
   if (cpha != PLATFORM_SPI_CPHA_LOW && cpha != PLATFORM_SPI_CPHA_HIGH) {
     return luaL_error( L, "wrong arg type" );