diff --git a/gc.c b/gc.c
index e67d1c0b8e..c10694d3f6 100644
--- a/gc.c
+++ b/gc.c
@@ -3397,7 +3397,17 @@ gc_count(rb_execution_context_t *ec, VALUE self)
 VALUE
 rb_gc_latest_gc_info(VALUE key)
 {
-    return rb_gc_impl_latest_gc_info(rb_gc_get_objspace(), key);
+    if (!SYMBOL_P(key) && !RB_TYPE_P(key, T_HASH)) {
+        rb_raise(rb_eTypeError, "non-hash or symbol given");
+    }
+
+    VALUE val = rb_gc_impl_latest_gc_info(rb_gc_get_objspace(), key);
+
+    if (val == Qundef) {
+        rb_raise(rb_eArgError, "unknown key: %"PRIsVALUE, rb_sym2str(key));
+    }
+
+    return val;
 }
 
 static VALUE
diff --git a/gc/default.c b/gc/default.c
index 50ad291081..2bb3d0512b 100644
--- a/gc/default.c
+++ b/gc/default.c
@@ -7291,7 +7291,7 @@ gc_info_decode(rb_objspace_t *objspace, const VALUE hash_or_key, const unsigned
         hash = hash_or_key;
     }
     else {
-        rb_raise(rb_eTypeError, "non-hash or symbol given");
+        rb_bug("gc_info_decode: non-hash or symbol given");
     }
 
     if (NIL_P(sym_major_by)) {
@@ -7377,8 +7377,9 @@ gc_info_decode(rb_objspace_t *objspace, const VALUE hash_or_key, const unsigned
     SET(retained_weak_references_count, LONG2FIX(objspace->profile.retained_weak_references_count));
 #undef SET
 
-    if (!NIL_P(key)) {/* matched key should return above */
-        rb_raise(rb_eArgError, "unknown key: %"PRIsVALUE, rb_sym2str(key));
+    if (!NIL_P(key)) {
+        // Matched key should return above
+        return Qundef;
     }
 
     return hash;