diff --git a/server/modules/filter/cache/rules.cc b/server/modules/filter/cache/rules.cc
index e7feb9f56..1983862f4 100644
--- a/server/modules/filter/cache/rules.cc
+++ b/server/modules/filter/cache/rules.cc
@@ -537,6 +537,7 @@ static CACHE_RULE *cache_rule_create_regexp(cache_rule_attribute_t attribute,
         pcre2_jit_compile(code, PCRE2_JIT_COMPLETE);
 
         int n_threads = config_threadcount();
+        ss_dassert(n_threads > 0);
 
         pcre2_match_data **datas = alloc_match_datas(n_threads, code);
 
diff --git a/server/modules/filter/cache/test/testrules.cc b/server/modules/filter/cache/test/testrules.cc
index 32f72cd2a..932b51870 100644
--- a/server/modules/filter/cache/test/testrules.cc
+++ b/server/modules/filter/cache/test/testrules.cc
@@ -236,6 +236,9 @@ int main()
 
     if (mxs_log_init(NULL, ".", MXS_LOG_TARGET_DEFAULT))
     {
+        MXS_CONFIG* pConfig = config_get_global_options();
+        pConfig->n_threads = 1;
+
         set_libdir(MXS_STRDUP_A("../../../../../query_classifier/qc_sqlite/"));
         if (qc_setup("qc_sqlite", "") && qc_process_init(QC_INIT_BOTH))
         {