diff --git a/cc.sh b/cc.sh
index 4156eed..a72aaa9 100755
--- a/cc.sh
+++ b/cc.sh
@@ -261,24 +261,10 @@ append_path_lists() {
     esac
 }
 
-# Check if optional parameters are defined
-# If we aren't asking for debug flags, don't add them
-if [ -z "${SPACK_ADD_DEBUG_FLAGS:-}" ]; then
-    SPACK_ADD_DEBUG_FLAGS="false"
-fi
-
-# SPACK_ADD_DEBUG_FLAGS must be true/false/custom
-is_valid="false"
-for param in "true" "false" "custom"; do
-  if [ "$param" = "$SPACK_ADD_DEBUG_FLAGS" ];  then
-      is_valid="true"
-  fi
-done
-
-# Exit with error if we are given an incorrect value
-if [ "$is_valid" = "false" ]; then
-    die "SPACK_ADD_DEBUG_FLAGS, if defined, must be one of 'true', 'false', or 'custom'."
-fi
+case "${SPACK_ADD_DEBUG_FLAGS:-false}" in
+    true|false|custom) ;;
+    *) die "SPACK_ADD_DEBUG_FLAGS must be true, false, or custom" ;;
+esac
 
 # Figure out the type of compiler, the language, and the mode so that
 # the compiler script knows what to do.
diff --git a/test/run.sh b/test/run.sh
index a59b0a9..bdacae3 100644
--- a/test/run.sh
+++ b/test/run.sh
@@ -1056,6 +1056,45 @@ hello.c')
     expect_contains frandom_seed_user_passthrough "$_out" '-frandom-seed=custom'
 }
 
+# ---------------------------------------------------------------------------
+# SPACK_ADD_DEBUG_FLAGS validation
+# ---------------------------------------------------------------------------
+
+test_add_debug_flags_validation() {
+    wrapper_environment
+    SPACK_TEST_COMMAND=dump-mode; export SPACK_TEST_COMMAND
+
+    # Unset and accepted values: wrapper should exit 0.
+    unset SPACK_ADD_DEBUG_FLAGS
+    _out=$("$WRAPPER_DIR/cc" -E 2>&1)
+    _rc=$?
+    if [ "$_rc" -ne 0 ]; then
+        fail "add_debug_flags_unset: unexpected exit $_rc, output: $_out"
+    fi
+
+    for _v in true false custom; do
+        SPACK_ADD_DEBUG_FLAGS=$_v; export SPACK_ADD_DEBUG_FLAGS
+        _out=$("$WRAPPER_DIR/cc" -E 2>&1)
+        _rc=$?
+        if [ "$_rc" -ne 0 ]; then
+            fail "add_debug_flags_${_v}: unexpected exit $_rc, output: $_out"
+        fi
+    done
+
+    # Invalid value: wrapper must die with a message mentioning the var.
+    SPACK_ADD_DEBUG_FLAGS=bogus; export SPACK_ADD_DEBUG_FLAGS
+    _out=$("$WRAPPER_DIR/cc" -E 2>&1)
+    _rc=$?
+    if [ "$_rc" -eq 0 ]; then
+        fail "add_debug_flags_invalid: expected non-zero exit, got 0"
+    fi
+    case "$_out" in
+        *SPACK_ADD_DEBUG_FLAGS*) ;;
+        *) fail "add_debug_flags_invalid: expected 'SPACK_ADD_DEBUG_FLAGS' in: $_out" ;;
+    esac
+    unset SPACK_ADD_DEBUG_FLAGS
+}
+
 # ---------------------------------------------------------------------------
 # Runner
 # ---------------------------------------------------------------------------
@@ -1076,6 +1115,7 @@ test_linker_strips_loopopt
 test_spack_managed_dirs_are_prioritized
 test_frandom_seed_not_added_without_env
 test_frandom_seed_filters_args
+test_add_debug_flags_validation
 '
 
 if [ $# -gt 0 ]; then