diff --git a/cli/core.c b/cli/core.c
index 44bdcca..840de42 100644
--- a/cli/core.c
+++ b/cli/core.c
@@ -351,7 +351,7 @@ apply_path(pkgconf_client_t *client, pkgconf_pkg_t *world, void *unused, int max
 }
 
 static bool
-apply_variable(pkgconf_client_t *client, pkgconf_pkg_t *world, void *variable, int maxdepth)
+apply_variable(pkgconf_client_t *client, pkgconf_pkg_t *world, const void *variable, int maxdepth)
 {
 	pkgconf_node_t *iter;
 	(void) maxdepth;
@@ -501,7 +501,7 @@ apply_env_variables(pkgconf_client_t *client, pkgconf_pkg_t *world, const char *
 }
 
 static bool
-apply_env(pkgconf_client_t *client, pkgconf_pkg_t *world, void *env_prefix_p, int maxdepth)
+apply_env(pkgconf_client_t *client, pkgconf_pkg_t *world, const void *env_prefix_p, int maxdepth)
 {
 	pkgconf_cli_state_t *state = client->client_data;
 	const char *want_env_prefix = env_prefix_p, *it;
diff --git a/cli/core.h b/cli/core.h
index 886678f..0cf5668 100644
--- a/cli/core.h
+++ b/cli/core.h
@@ -77,9 +77,9 @@ typedef struct {
 	int maximum_traverse_depth;
 	size_t maximum_package_count;
 
-	char *want_variable;
-	char *want_fragment_filter;
-	char *want_env_prefix;
+	const char *want_variable;
+	const char *want_fragment_filter;
+	const char *want_env_prefix;
 
 	char *required_pkgconfig_version;
 	char *required_exact_module_version;
diff --git a/tests/test-runner.c b/tests/test-runner.c
index 7d19dbd..370427a 100644
--- a/tests/test-runner.c
+++ b/tests/test-runner.c
@@ -41,6 +41,8 @@ typedef struct test_case_ {
 	uint64_t wanted_flags;
 
 	pkgconf_list_t env_vars;
+
+	pkgconf_buffer_t want_env_prefix;
 } pkgconf_test_case_t;
 
 typedef struct test_state_ {
@@ -345,6 +347,7 @@ static const pkgconf_test_keyword_pair_t test_keyword_pairs[] = {
 	{"PackageSearchPath", test_keyword_set_path_list, offsetof(pkgconf_test_case_t, search_path)},
 	{"Query", test_keyword_set_buffer, offsetof(pkgconf_test_case_t, query)},
 	{"WantedFlags", test_keyword_set_wanted_flags, offsetof(pkgconf_test_case_t, wanted_flags)},
+	{"WantEnvPrefix", test_keyword_set_buffer, offsetof(pkgconf_test_case_t, want_env_prefix)},
 };
 
 static void
@@ -517,10 +520,12 @@ annotate_result(const pkgconf_test_case_t *testcase, int ret, const pkgconf_test
 	fprintf(stderr,
 		"stderr: [%s]\n"
 		"expected-stderr: [%s] (%s)\n"
+		"want-env-prefix: [%s]\n"
 		"--------------------------------------------------------------------------------\n",
 		pkgconf_buffer_str_or_empty(&out->o_stderr),
 		pkgconf_buffer_str_or_empty(&testcase->expected_stderr),
-		testcase->match_stderr == MATCH_PARTIAL ? "partial" : "exact");
+		testcase->match_stderr == MATCH_PARTIAL ? "partial" : "exact",
+		pkgconf_buffer_str_or_empty(&testcase->want_env_prefix));
 
 	pkgconf_buffer_finalize(&search_path_buf);
 	pkgconf_buffer_finalize(&wanted_flags_buf);
@@ -535,6 +540,7 @@ run_test_case(const pkgconf_test_case_t *testcase)
 	pkgconf_cross_personality_t *personality = personality_for_test(testcase);
 	pkgconf_test_state_t state = {
 		.cli_state.want_flags = testcase->wanted_flags,
+		.cli_state.want_env_prefix = pkgconf_buffer_str(&testcase->want_env_prefix),
 		.testcase = testcase,
 	};