diff --git a/gc.c b/gc.c
index 66cdb2cd4b..41d3d6aba4 100644
--- a/gc.c
+++ b/gc.c
@@ -1245,6 +1245,8 @@ rb_gc_obj_free_vm_weak_references(VALUE obj)
     switch (BUILTIN_TYPE(obj)) {
       case T_STRING:
         if (FL_TEST(obj, RSTRING_FSTR)) {
+            RUBY_ASSERT(!FL_TEST(obj, STR_SHARED));
+
             st_data_t fstr = (st_data_t)obj;
             st_delete(rb_vm_fstring_table(), &fstr, NULL);
             RB_DEBUG_COUNTER_INC(obj_str_fstr);
diff --git a/string.c b/string.c
index 916b675bc8..7a9392d6ae 100644
--- a/string.c
+++ b/string.c
@@ -1500,7 +1500,7 @@ rb_str_tmp_frozen_no_embed_acquire(VALUE orig)
      * allocated. If the string is shared then the shared root must be
      * embedded, so we want to create a copy. If the string is a shared root
      * then it must be embedded, so we want to create a copy. */
-    if (STR_EMBED_P(orig) || FL_TEST_RAW(orig, STR_SHARED | STR_SHARED_ROOT)) {
+    if (STR_EMBED_P(orig) || FL_TEST_RAW(orig, STR_SHARED | STR_SHARED_ROOT | RSTRING_FSTR)) {
         RSTRING(str)->as.heap.ptr = rb_xmalloc_mul_add_mul(sizeof(char), capa, sizeof(char), TERM_LEN(orig));
         memcpy(RSTRING(str)->as.heap.ptr, RSTRING_PTR(orig), capa);
     }
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 0c75852093..f7009b518e 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -3438,6 +3438,15 @@ CODE
     assert_equal(false, str.frozen?)
   end
 
+  def test_uminus_no_embed_gc
+    pad = "a"*2048
+    ("aa".."zz").each do |c|
+      fstr = -(c + pad).freeze
+      File.open(IO::NULL, "w").write(fstr)
+    end
+    GC.start
+  end
+
   def test_ord
     assert_equal(97, S("a").ord)
     assert_equal(97, S("abc").ord)