diff --git a/src/compiler/clc/clc.h b/src/compiler/clc/clc.h
index 690c3db0a45..de867cf1d6c 100644
--- a/src/compiler/clc/clc.h
+++ b/src/compiler/clc/clc.h
@@ -49,6 +49,7 @@ enum clc_spirv_version {
    CLC_SPIRV_VERSION_1_4,
 };
 
+// IMPORTANT: this struct is used for hashing and must not contain any padding.
 struct clc_optional_features {
    bool fp16;
    bool fp64;