diff --git a/.github/workflows/modgc.yml b/.github/workflows/modgc.yml
index d0a980700821a8..6cf4760a1d3cc5 100644
--- a/.github/workflows/modgc.yml
+++ b/.github/workflows/modgc.yml
@@ -137,8 +137,14 @@ jobs:
         if: ${{ matrix.test_task == 'check' && matrix.skipped_tests }}
 
       - name: Set timeout scale
-        run: echo "RUBY_TEST_TIMEOUT_SCALE=10" >> $GITHUB_ENV # subprocess assertion timeouts flake on slower/contended macOS runners, especially with the slower MMTk GC
-        if: ${{ contains(matrix.os, 'macos') }}
+        run: |
+          scale=$((os_scale * gc_scale))
+          echo "RUBY_TEST_TIMEOUT_SCALE=$scale" >> "$GITHUB_ENV"
+        env:
+          # Subprocess assertion timeouts flake on slower or contended macOS
+          # runners and with the slower MMTk GC.
+          os_scale: ${{ contains(matrix.os, 'macos') && 3 || 1 }}
+          gc_scale: ${{ matrix.gc.name == 'mmtk' && 3 || 1 }}
 
       - name: Set up Launchable
         id: launchable
diff --git a/ext/strscan/strscan.c b/ext/strscan/strscan.c
index da02291478c3c4..1894ed7fb3088a 100644
--- a/ext/strscan/strscan.c
+++ b/ext/strscan/strscan.c
@@ -1862,8 +1862,13 @@ strscan_integer_at(int argc, VALUE *argv, VALUE self)
         return Qnil;
 
     beg = adjust_register_position(p, p->regs.beg[i]);
+    if (beg > S_LEN(p))
+        return Qnil;
     end = adjust_register_position(p, p->regs.end[i]);
+    end = minl(end, S_LEN(p));
     len = end - beg;
+    if (len == 0)
+        return Qnil;
     ptr = S_PBEG(p) + beg;
 #ifdef HAVE_RB_INT_PARSE_CSTR
     {
diff --git a/test/strscan/test_stringscanner.rb b/test/strscan/test_stringscanner.rb
index 96a1badb1f1087..966d62b22689b8 100644
--- a/test/strscan/test_stringscanner.rb
+++ b/test/strscan/test_stringscanner.rb
@@ -578,6 +578,26 @@ def test_integer_at_base_auto
     assert_integer_at(s, 0, 0) # 0xaf
   end
 
+  def test_integer_at_shrunk
+    omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"
+
+    s = create_string_scanner(+"before 29 after")
+    s.skip_until(" ")
+    assert_equal("29", s.scan(/\d+/))
+    s.string.replace("before ")
+    assert_nil(s.integer_at(0))
+  end
+
+  def test_integer_at_shrunk_partial
+    omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"
+
+    s = create_string_scanner(+"before 29 after")
+    s.skip_until(" ")
+    assert_equal("29", s.scan(/\d+/))
+    s.string.replace("before 2")
+    assert_integer_at(s, 2)
+  end
+
   def test_pre_match
     s = create_string_scanner('a b c d e')
     s.scan(/\w/)
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index 4f95c10bcb5690..d7b2218d9b7a06 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -952,6 +952,7 @@ s,@SHELL@,$$(COMSPEC),;t t
 s,@BUILD_FILE_SEPARATOR@,\,;t t
 s,@PATH_SEPARATOR@,;,;t t
 s,@CFLAGS@,$(CFLAGS),;t t
+s,@warnflags@,$(WARNFLAGS),;t t
 s,@WERRORFLAG@,$(WERRORFLAG),;t t
 s,@DEFS@,$(DEFS),;t t
 s,@CPPFLAGS@,$(CPPFLAGS),;t t