diff --git a/cachedb/cachedb.c b/cachedb/cachedb.c
index 4e26c837e..b4f2bda0f 100644
--- a/cachedb/cachedb.c
+++ b/cachedb/cachedb.c
@@ -61,6 +61,8 @@
 /** the unit test testframe for cachedb, its module state contains
  * a cache for a couple queries (in memory). */
 struct testframe_moddata {
+	/** lock for mutex */
+	lock_basic_type lock;
 	/** key for single stored data element, NULL if none */
 	char* stored_key;
 	/** data for single stored data element, NULL if none */
@@ -72,14 +74,17 @@ struct testframe_moddata {
 static int
 testframe_init(struct module_env* env, struct cachedb_env* cachedb_env)
 {
+	struct testframe_moddata* d;
 	(void)env;
 	verbose(VERB_ALGO, "testframe_init");
-	cachedb_env->backend_data = (void*)calloc(1,
+	d = (struct testframe_moddata*)calloc(1,
 		sizeof(struct testframe_moddata));
+	cachedb_env->backend_data = (void*)d;
 	if(!cachedb_env->backend_data) {
 		log_err("out of memory");
 		return 0;
 	}
+	lock_basic_init(&d->lock);
 	return 1;
 }
 
@@ -92,6 +97,7 @@ testframe_deinit(struct module_env* env, struct cachedb_env* cachedb_env)
 	verbose(VERB_ALGO, "testframe_deinit");
 	if(!d)
 		return;
+	lock_basic_destroy(&d->lock);
 	free(d->stored_key);
 	free(d->stored_data);
 	free(d);
@@ -105,17 +111,22 @@ testframe_lookup(struct module_env* env, struct cachedb_env* cachedb_env,
 		cachedb_env->backend_data;
 	(void)env;
 	verbose(VERB_ALGO, "testframe_lookup of %s", key);
+	lock_basic_lock(&d->lock);
 	if(d->stored_key && strcmp(d->stored_key, key) == 0) {
-		if(d->stored_datalen > sldns_buffer_capacity(result_buffer))
+		if(d->stored_datalen > sldns_buffer_capacity(result_buffer)) {
+			lock_basic_unlock(&d->lock);
 			return 0; /* too large */
+		}
 		verbose(VERB_ALGO, "testframe_lookup found %d bytes",
 			(int)d->stored_datalen);
 		sldns_buffer_clear(result_buffer);
 		sldns_buffer_write(result_buffer, d->stored_data,
 			d->stored_datalen);
 		sldns_buffer_flip(result_buffer);
+		lock_basic_unlock(&d->lock);
 		return 1;
 	}
+	lock_basic_unlock(&d->lock);
 	return 0;
 }
 
@@ -126,6 +137,7 @@ testframe_store(struct module_env* env, struct cachedb_env* cachedb_env,
 	struct testframe_moddata* d = (struct testframe_moddata*)
 		cachedb_env->backend_data;
 	(void)env;
+	lock_basic_lock(&d->lock);
 	verbose(VERB_ALGO, "testframe_store %s (%d bytes)", key, (int)data_len);
 
 	/* free old data element (if any) */
@@ -137,6 +149,7 @@ testframe_store(struct module_env* env, struct cachedb_env* cachedb_env,
 
 	d->stored_data = memdup(data, data_len);
 	if(!d->stored_data) {
+		lock_basic_unlock(&d->lock);
 		log_err("out of memory");
 		return;
 	}
@@ -146,8 +159,10 @@ testframe_store(struct module_env* env, struct cachedb_env* cachedb_env,
 		free(d->stored_data);
 		d->stored_data = NULL;
 		d->stored_datalen = 0;
+		lock_basic_unlock(&d->lock);
 		return;
 	}
+	lock_basic_unlock(&d->lock);
 	/* (key,data) successfully stored */
 }
 
diff --git a/doc/Changelog b/doc/Changelog
index e4c323679..d5fc4c906 100644
--- a/doc/Changelog
+++ b/doc/Changelog
@@ -1,3 +1,6 @@
+31 August 2017: Wouter
+	- Fix #1424: cachedb:testframe is not thread safe.
+
 30 August 2017: Wouter
 	- updated contrib/fastrpz.patch to apply with configparser changes.
 	- Fix 1416: qname-minimisation breaks TLSA lookups with CNAMEs.