diff --git a/common/test/run-gossmap_local.c b/common/test/run-gossmap_local.c
index e2a198f54..20b08d562 100644
--- a/common/test/run-gossmap_local.c
+++ b/common/test/run-gossmap_local.c
@@ -7,6 +7,7 @@
 #include <ccan/read_write_all/read_write_all.h>
 #include <common/channel_type.h>
 #include <common/setup.h>
+#include <common/utils.h>
 #include <stdio.h>
 
 /* AUTOGENERATED MOCKS START */
@@ -292,7 +293,7 @@ static void check_nannounce(const u8 *nannounce,
 int main(int argc, char *argv[])
 {
 	int fd;
-	char gossfile[] = "/tmp/run-gossip_local.XXXXXX";
+	char *gossfile;
 	struct gossmap *map;
 	struct node_id l1, l2, l3, l4;
 	struct short_channel_id scid23, scid12, scid_local;
@@ -306,7 +307,7 @@ int main(int argc, char *argv[])
 
 	common_setup(argv[0]);
 
-	fd = mkstemp(gossfile);
+	fd = tmpdir_mkstemp(tmpctx, "run-gossip_local.XXXXXX", &gossfile);
 	assert(write_all(fd, canned_map, sizeof(canned_map)));
 
 	map = gossmap_load(tmpctx, gossfile, NULL);
diff --git a/common/test/run-route-specific.c b/common/test/run-route-specific.c
index 4451e51ae..33ab55dce 100644
--- a/common/test/run-route-specific.c
+++ b/common/test/run-route-specific.c
@@ -13,6 +13,7 @@
 #include <common/route.h>
 #include <common/setup.h>
 #include <common/type_to_string.h>
+#include <common/utils.h>
 #include <bitcoin/chainparams.h>
 #include <stdio.h>
 #include <wire/peer_wiregen.h>
@@ -185,7 +186,7 @@ int main(int argc, char *argv[])
 	struct gossmap *gossmap;
 	const double riskfactor = 1.0;
 	char gossip_version = GOSSIP_STORE_VERSION;
-	char gossipfilename[] = "/tmp/run-route-specific-gossipstore.XXXXXX";
+	char *gossipfilename;
 
 	common_setup(argv[0]);
 	node_id_from_hexstr("03c173897878996287a8100469f954dd820fcd8941daed91c327f168f3329be0bf",
@@ -203,7 +204,7 @@ int main(int argc, char *argv[])
 
 	chainparams = chainparams_for_network("regtest");
 
-	store_fd = mkstemp(gossipfilename);
+	store_fd = tmpdir_mkstemp(tmpctx, "run-route-specific-gossipstore.XXXXXX", &gossipfilename);
 	assert(write(store_fd, &gossip_version, sizeof(gossip_version))
 	       == sizeof(gossip_version));
 
diff --git a/common/test/run-route.c b/common/test/run-route.c
index 07dd66e3d..0db4d77d9 100644
--- a/common/test/run-route.c
+++ b/common/test/run-route.c
@@ -6,6 +6,7 @@
 #include <common/route.h>
 #include <common/setup.h>
 #include <common/type_to_string.h>
+#include <common/utils.h>
 #include <bitcoin/chainparams.h>
 #include <stdio.h>
 #include <wire/peer_wiregen.h>
@@ -182,11 +183,11 @@ int main(int argc, char *argv[])
 	struct gossmap *gossmap;
 	const double riskfactor = 1.0;
 	char gossip_version = GOSSIP_STORE_VERSION;
-	char gossipfilename[] = "/tmp/run-route-gossipstore.XXXXXX";
+	char *gossipfilename;
 
 	chainparams = chainparams_for_network("regtest");
 
-	store_fd = mkstemp(gossipfilename);
+	store_fd = tmpdir_mkstemp(tmpctx, "run-route-gossipstore.XXXXXX", &gossipfilename);
 	assert(write(store_fd, &gossip_version, sizeof(gossip_version))
 	       == sizeof(gossip_version));
 	gossmap = gossmap_load(tmpctx, gossipfilename, NULL);
diff --git a/common/utils.c b/common/utils.c
index 311de3e0a..57bc8f02e 100644
--- a/common/utils.c
+++ b/common/utils.c
@@ -2,6 +2,7 @@
 #include <bitcoin/chainparams.h>
 #include <ccan/list/list.h>
 #include <ccan/str/hex/hex.h>
+#include <ccan/tal/path/path.h>
 #include <ccan/utf8/utf8.h>
 #include <errno.h>
 #include <locale.h>
@@ -217,3 +218,17 @@ char *utf8_str(const tal_t *ctx, const u8 *buf TAKES, size_t buflen)
 	ret[buflen] = '\0';
 	return ret;
 }
+
+int tmpdir_mkstemp(const tal_t *ctx, const char *template TAKES, char **created)
+{
+	char *tmpdir = getenv("TMPDIR");
+	char *path = path_join(ctx, tmpdir ?: "/tmp", template);
+	int fd = mkstemp(path);
+
+	if (fd >= 0)
+		*created = path;
+	else
+		tal_free(path);
+
+	return fd;
+}
diff --git a/common/utils.h b/common/utils.h
index 0282f5a53..66ca58a4d 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -152,4 +152,8 @@ STRUCTEQ_DEF(ripemd160, 0, u);
 /* Context which all wally allocations use (see common/setup.c) */
 extern const tal_t *wally_tal_ctx;
 
+/* Like mkstemp but resolves template relative to $TMPDIR (or /tmp if unset).
+ * Returns created temporary path name at *created if successful. */
+int tmpdir_mkstemp(const tal_t *ctx, const char *template TAKES, char **created);
+
 #endif /* LIGHTNING_COMMON_UTILS_H */
diff --git a/plugins/test/run-route-overlong.c b/plugins/test/run-route-overlong.c
index c4abb47e5..ce67a15a9 100644
--- a/plugins/test/run-route-overlong.c
+++ b/plugins/test/run-route-overlong.c
@@ -2,6 +2,7 @@
 #include <bitcoin/chainparams.h>
 #include <common/gossip_store.h>
 #include <common/setup.h>
+#include <common/utils.h>
 #include <stdio.h>
 #include <unistd.h>
 
@@ -332,11 +333,11 @@ int main(int argc, char *argv[])
 	struct payment *p;
 	struct payment_modifier **mods;
 	char gossip_version = GOSSIP_STORE_VERSION;
-	char gossipfilename[] = "/tmp/run-route-overlong.XXXXXX";
+	char *gossipfilename;
 
 	common_setup(argv[0]);
 	chainparams = chainparams_for_network("regtest");
-	store_fd = mkstemp(gossipfilename);
+	store_fd = tmpdir_mkstemp(tmpctx, "run-route-overlong.XXXXXX", &gossipfilename);
 	assert(write(store_fd, &gossip_version, sizeof(gossip_version))
 	       == sizeof(gossip_version));
 
diff --git a/wallet/test/run-db.c b/wallet/test/run-db.c
index c6123e9ab..9f7e17d6a 100644
--- a/wallet/test/run-db.c
+++ b/wallet/test/run-db.c
@@ -13,6 +13,7 @@ static void db_log_(struct log *log UNUSED, enum log_level level UNUSED, const s
 #include "test_utils.h"
 
 #include <common/setup.h>
+#include <common/utils.h>
 #include <stdio.h>
 #include <unistd.h>
 
@@ -76,14 +77,15 @@ void plugin_hook_db_sync(struct db *db UNNEEDED)
 static struct db *create_test_db(void)
 {
 	struct db *db;
-	char *dsn, filename[] = "/tmp/ldb-XXXXXX";
+	char *dsn, *filename;
 
-	int fd = mkstemp(filename);
+	int fd = tmpdir_mkstemp(tmpctx, "ldb-XXXXXX", &filename);
 	if (fd == -1)
 		return NULL;
 	close(fd);
 
 	dsn = tal_fmt(NULL, "sqlite3://%s", filename);
+	tal_free(filename);
 	db = db_open(NULL, dsn);
 	db->data_version = 0;
 	tal_free(dsn);
diff --git a/wallet/test/run-wallet.c b/wallet/test/run-wallet.c
index e5b170ccd..43425ab05 100644
--- a/wallet/test/run-wallet.c
+++ b/wallet/test/run-wallet.c
@@ -18,6 +18,7 @@ static void db_log_(struct log *log UNUSED, enum log_level level UNUSED, const s
 #include "wallet/db.c"
 
 #include <common/setup.h>
+#include <common/utils.h>
 #include <stdio.h>
 
 bool deprecated_apis = true;
@@ -917,8 +918,8 @@ static void cleanup_test_wallet(struct wallet *w, char *filename)
 
 static struct wallet *create_test_wallet(struct lightningd *ld, const tal_t *ctx)
 {
-	char *dsn, *filename = tal_fmt(ctx, "/tmp/ldb-XXXXXX");
-	int fd = mkstemp(filename);
+	char *dsn, *filename;
+	int fd = tmpdir_mkstemp(ctx, "ldb-XXXXXX", &filename);
 	struct wallet *w = tal(ctx, struct wallet);
 	static unsigned char badseed[BIP32_ENTROPY_LEN_128];
 	const struct ext_key *bip32_base = NULL;