3 files changed, 58 insertions, 5 deletions

diff --git a/gc.c b/gc.c
index 9471a95354..6a81a5e4b3 100644
--- a/gc.c
+++ b/gc.c
@@ -11954,12 +11954,47 @@ wmap_mark_map(st_data_t key, st_data_t val, st_data_t arg)
 }
 #endif
 
+static int
+wmap_replace_ref(st_data_t *key, st_data_t *value, st_data_t _argp, int existing)
+{
+    *key = rb_gc_location((VALUE)*key);
+
+    VALUE *values = (VALUE *)*value;
+    VALUE size = values[0];
+
+    for (VALUE index = 1; index <= size; index++) {
+        values[index] = rb_gc_location(values[index]);
+    }
+
+    return ST_CONTINUE;
+}
+
+static int
+wmap_foreach_replace(st_data_t key, st_data_t value, st_data_t _argp, int error)
+{
+    if (rb_gc_location((VALUE)key) != (VALUE)key) {
+        return ST_REPLACE;
+    }
+
+    VALUE *values = (VALUE *)value;
+    VALUE size = values[0];
+
+    for (VALUE index = 1; index <= size; index++) {
+        VALUE val = values[index];
+        if (rb_gc_location(val) != val) {
+            return ST_REPLACE;
+        }
+    }
+
+    return ST_CONTINUE;
+}
+
 static void
 wmap_compact(void *ptr)
 {
     struct weakmap *w = ptr;
     if (w->wmap2obj) rb_gc_update_tbl_refs(w->wmap2obj);
-    if (w->obj2wmap) rb_gc_update_tbl_refs(w->obj2wmap);
+    if (w->obj2wmap) st_foreach_with_replace(w->obj2wmap, wmap_foreach_replace, wmap_replace_ref, (st_data_t)NULL);
     w->final = rb_gc_location(w->final);
 }
 
@@ -12072,9 +12107,9 @@ wmap_final_func(st_data_t *key, st_data_t *value, st_data_t arg, int existing)
 	return ST_DELETE;
     }
     if (j < i) {
-        SIZED_REALLOC_N(ptr, VALUE, j + 1, i);
-	ptr[0] = j;
-	*value = (st_data_t)ptr;
+        SIZED_REALLOC_N(ptr, VALUE, j, i);
+        ptr[0] = j - 1;
+        *value = (st_data_t)ptr;
     }
     return ST_CONTINUE;
 }
diff --git a/test/ruby/test_weakmap.rb b/test/ruby/test_weakmap.rb
index c482f697c3..5ca6b0fbdd 100644
--- a/test/ruby/test_weakmap.rb
+++ b/test/ruby/test_weakmap.rb
@@ -176,4 +176,22 @@ class TestWeakMap < Test::Unit::TestCase
       end
     end;
   end
+
+  def test_compaction_bug_19529
+    obj = Object.new
+    100.times do |i|
+      GC.compact
+      @wm[i] = obj
+    end
+
+    assert_separately(%w(--disable-gems), <<-'end;')
+      wm = ObjectSpace::WeakMap.new
+      obj = Object.new
+      100.times do
+        wm[Object.new] = obj
+        GC.start
+      end
+      GC.compact
+    end;
+  end
 end
diff --git a/version.h b/version.h
index 9bcaa82d62..114ab90195 100644
--- a/version.h
+++ b/version.h
@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 4
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 217
+#define RUBY_PATCHLEVEL 218
 
 #define RUBY_RELEASE_YEAR 2023
 #define RUBY_RELEASE_MONTH 3