diff --git a/pkgs/development/compilers/crystal/default.nix b/pkgs/development/compilers/crystal/default.nix
index db22b668cf5..8f75692d883 100644
--- a/pkgs/development/compilers/crystal/default.nix
+++ b/pkgs/development/compilers/crystal/default.nix
@@ -108,6 +108,8 @@ let
       "all" "docs"
     ];
 
+    LLVM_CONFIG = "${llvm}/bin/llvm-config";
+
     FLAGS = [
       "--release"
       "--single-module" # needed for deterministic builds