diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 15d483b858..9081338b3e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -73,6 +73,9 @@ jobs:
           name: gem-${{ matrix.os }}-${{ matrix.ruby }}
           path: pkg/
 
+      - run: echo 'TESTOPTS=-v --ignore-name=/unscan/' >> $GITHUB_ENV
+        if: ${{ startsWith(matrix.ruby, 'truffle') }}
+
       - run: bundle exec rake test
 
       - run: gem install --verbose --backtrace pkg/*.gem
@@ -80,5 +83,5 @@ jobs:
       - run: gem install test-unit-ruby-core test-unit
 
       - name: Run tests on the installed gem
-        run: ruby run-test.rb
+        run: ruby run-test.rb ${TESTOPTS}
         if: matrix.ruby != '2.4' # strscan is a default gem from 2.5
diff --git a/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java b/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
index 5a385c01e0..03a496ae50 100644
--- a/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
+++ b/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
@@ -83,21 +83,23 @@ public class RubyStringScanner extends RubyObject {
 
     public static RubyClass createScannerClass(final Ruby runtime) {
         RubyClass Object = runtime.getObject();
+        ThreadContext context = runtime.getCurrentContext();
 
         RubyClass scannerClass = runtime.defineClass("StringScanner", Object, RubyStringScanner::new);
 
         RubyClass standardError = runtime.getStandardError();
-        RubyClass error = scannerClass.defineClassUnder("Error", standardError, standardError.getAllocator());
-        if (!Object.isConstantDefined("ScanError")) {
-            Object.defineConstant("ScanError", error);
+        RubyClass error = scannerClass.defineClassUnder(context, "Error", standardError, standardError.getAllocator());
+        if (!Object.isConstantDefined(context, "ScanError")) {
+            Object.defineConstant(context, "ScanError", error);
+            Object.deprecateConstant(context, "ScanError");
         }
 
         RubyString version = runtime.newString(STRSCAN_VERSION);
         version.setFrozen(true);
-        scannerClass.setConstant("Version", version);
+        scannerClass.setConstant(context, "Version", version);
         RubyString id = runtime.newString("$Id$");
         id.setFrozen(true);
-        scannerClass.setConstant("Id", id);
+        scannerClass.setConstant(context, "Id", id);
 
         scannerClass.defineAnnotatedMethods(RubyStringScanner.class);
 
diff --git a/ext/strscan/extconf.rb b/ext/strscan/extconf.rb
index 3c311d2364..d2e9343cbc 100644
--- a/ext/strscan/extconf.rb
+++ b/ext/strscan/extconf.rb
@@ -4,6 +4,7 @@
   $INCFLAGS << " -I$(top_srcdir)" if $extmk
   have_func("onig_region_memsize(NULL)")
   have_func("rb_reg_onig_match", "ruby/re.h")
+  have_func("rb_deprecate_constant")
   create_makefile 'strscan'
 else
   File.write('Makefile', dummy_makefile("").join)
diff --git a/ext/strscan/strscan.c b/ext/strscan/strscan.c
index 93ba9da955..5cb14e88af 100644
--- a/ext/strscan/strscan.c
+++ b/ext/strscan/strscan.c
@@ -24,6 +24,14 @@ extern size_t onig_region_memsize(const struct re_registers *regs);
 
 #define STRSCAN_VERSION "3.1.6"
 
+
+#ifdef HAVE_RB_DEPRECATE_CONSTANT
+/* In ruby 3.0, defined but exposed in external headers */
+extern void rb_deprecate_constant(VALUE mod, const char *name);
+#else
+# define rb_deprecate_constant(mod, name) ((void)0)
+#endif
+
 /* =======================================================================
                          Data Type Definitions
    ======================================================================= */
@@ -1604,7 +1612,7 @@ name_to_backref_number(struct re_registers *regs, VALUE regexp, const char* name
                                               (const unsigned char* )name_end,
                                               regs);
         if (num >= 1) {
-	        return num;
+	    return num;
         }
     }
     rb_enc_raise(enc, rb_eIndexError, "undefined group name reference: %.*s",
@@ -2210,6 +2218,7 @@ Init_strscan(void)
     ScanError = rb_define_class_under(StringScanner, "Error", rb_eStandardError);
     if (!rb_const_defined(rb_cObject, id_scanerr)) {
 	rb_const_set(rb_cObject, id_scanerr, ScanError);
+	rb_deprecate_constant(rb_cObject, "ScanError");
     }
     tmp = rb_str_new2(STRSCAN_VERSION);
     rb_obj_freeze(tmp);
diff --git a/test/strscan/test_stringscanner.rb b/test/strscan/test_stringscanner.rb
index 085a911313..8218e5b6be 100644
--- a/test/strscan/test_stringscanner.rb
+++ b/test/strscan/test_stringscanner.rb
@@ -875,7 +875,7 @@ def test_unscan
     assert_equal({}, s.named_captures)
     assert_equal("te", s.scan(/../))
     assert_equal(nil, s.scan(/\d/))
-    assert_raise(ScanError) { s.unscan }
+    assert_raise(StringScanner::Error) { s.unscan }
   end
 
   def test_rest