diff --git a/src/core/symcache.c b/src/core/symcache.c
index 841bfbd9..a45e3202 100644
--- a/src/core/symcache.c
+++ b/src/core/symcache.c
@@ -233,8 +233,8 @@ const uint8_t *janet_symbol_gen(void) {
     head->length = sizeof(janet_vm.gensym_counter) - 1;
     head->hash = hash;
     sym = (uint8_t *)(head->data);
-    sym[head->length] = 0;
     memcpy(sym, janet_vm.gensym_counter, sizeof(janet_vm.gensym_counter));
+    sym[head->length] = 0;
     janet_symcache_put((const uint8_t *)sym, bucket);
     return (const uint8_t *)sym;
 }
diff --git a/test/suite-ev.janet b/test/suite-ev.janet
index a696f4ff..e65f2772 100644
--- a/test/suite-ev.janet
+++ b/test/suite-ev.janet
@@ -366,4 +366,10 @@
                (exec-slurp ;run janet "-e" "(print :hi)")))
           "exec-slurp 1"))
 
+# valgrind-able check for #1337
+(def superv (ev/chan 10))
+(def f (ev/go |(ev/sleep 1e9) nil superv))
+(ev/cancel f (gensym))
+(ev/take superv)
+
 (end-suite)