diff --git a/ext/json/ext/generator/generator.c b/ext/json/ext/generator/generator.c
index cb054532..c35e86d9 100644
--- a/ext/json/ext/generator/generator.c
+++ b/ext/json/ext/generator/generator.c
@@ -5,9 +5,9 @@
 #define RB_UNLIKELY(cond) (cond)
 #endif
 
-static VALUE mJSON, cState, mString_Extend, eGeneratorError, eNestingError;
+static VALUE mJSON, cState, mString_Extend, eGeneratorError, eNestingError, Encoding_UTF_8;
 
-static ID i_to_s, i_to_json, i_new, i_pack, i_unpack, i_create_id, i_extend;
+static ID i_to_s, i_to_json, i_new, i_pack, i_unpack, i_create_id, i_extend, i_encode;
 
 /* Converts in_string to a JSON string (without the wrapping '"'
  * characters) in FBuffer out_buffer.
@@ -735,20 +735,41 @@ static void generate_json_array(FBuffer *buffer, VALUE Vstate, JSON_Generator_St
     fbuffer_append_char(buffer, ']');
 }
 
-static int usascii_encindex, utf8_encindex;
+static int usascii_encindex, utf8_encindex, binary_encindex;
 
-static int enc_utf8_compatible_p(int enc_idx)
+static inline int enc_utf8_compatible_p(int enc_idx)
 {
     if (enc_idx == usascii_encindex) return 1;
     if (enc_idx == utf8_encindex) return 1;
     return 0;
 }
 
+static inline VALUE ensure_valid_encoding(VALUE str)
+{
+    int encindex = RB_ENCODING_GET(str);
+    VALUE utf8_string;
+    if (RB_UNLIKELY(!enc_utf8_compatible_p(encindex))) {
+        if (encindex == binary_encindex) {
+            // For historical reason, we silently reinterpret binary strings as UTF-8 if it would work.
+            // TODO: Deprecate in 2.8.0
+            // TODO: Remove in 3.0.0
+            utf8_string = rb_enc_associate_index(rb_str_dup(str), utf8_encindex);
+            switch (rb_enc_str_coderange(utf8_string)) {
+                case ENC_CODERANGE_7BIT:
+                case ENC_CODERANGE_VALID:
+                    return utf8_string;
+                    break;
+            }
+        }
+
+        str = rb_funcall(str, i_encode, 1, Encoding_UTF_8);
+    }
+    return str;
+}
+
 static void generate_json_string(FBuffer *buffer, VALUE Vstate, JSON_Generator_State *state, VALUE obj)
 {
-    if (!enc_utf8_compatible_p(RB_ENCODING_GET(obj))) {
-        obj = rb_str_export_to_enc(obj, rb_utf8_encoding());
-    }
+    obj = ensure_valid_encoding(obj);
 
     fbuffer_append_char(buffer, '"');
 
@@ -1462,6 +1483,9 @@ void Init_generator(void)
     VALUE mNilClass = rb_define_module_under(mGeneratorMethods, "NilClass");
     rb_define_method(mNilClass, "to_json", mNilClass_to_json, -1);
 
+    rb_global_variable(&Encoding_UTF_8);
+    Encoding_UTF_8 = rb_const_get(rb_path2class("Encoding"), rb_intern("UTF_8"));
+
     i_to_s = rb_intern("to_s");
     i_to_json = rb_intern("to_json");
     i_new = rb_intern("new");
@@ -1469,7 +1493,9 @@ void Init_generator(void)
     i_unpack = rb_intern("unpack");
     i_create_id = rb_intern("create_id");
     i_extend = rb_intern("extend");
+    i_encode = rb_intern("encode");
 
     usascii_encindex = rb_usascii_encindex();
     utf8_encindex = rb_utf8_encindex();
+    binary_encindex = rb_ascii8bit_encindex();
 }
diff --git a/ext/json/ext/parser/parser.c b/ext/json/ext/parser/parser.c
index 62effbd0..cf0b3cef 100644
--- a/ext/json/ext/parser/parser.c
+++ b/ext/json/ext/parser/parser.c
@@ -1794,6 +1794,9 @@ static VALUE convert_encoding(VALUE source)
   }
 
  if (encindex == binary_encindex) {
+    // For historical reason, we silently reinterpret binary strings as UTF-8 if it would work.
+    // TODO: Deprecate in 2.8.0
+    // TODO: Remove in 3.0.0
     return rb_enc_associate_index(rb_str_dup(source), utf8_encindex);
   }
 
@@ -1943,7 +1946,7 @@ static VALUE cParser_initialize(int argc, VALUE *argv, VALUE self)
 }
 
 
-#line 1947 "parser.c"
+#line 1950 "parser.c"
 enum {JSON_start = 1};
 enum {JSON_first_final = 10};
 enum {JSON_error = 0};
@@ -1951,7 +1954,7 @@ enum {JSON_error = 0};
 enum {JSON_en_main = 1};
 
 
-#line 855 "parser.rl"
+#line 858 "parser.rl"
 
 
 /*
@@ -1969,16 +1972,16 @@ static VALUE cParser_parse(VALUE self)
     GET_PARSER;
 
 
-#line 1973 "parser.c"
+#line 1976 "parser.c"
 	{
 	cs = JSON_start;
 	}
 
-#line 872 "parser.rl"
+#line 875 "parser.rl"
     p = json->source;
     pe = p + json->len;
 
-#line 1982 "parser.c"
+#line 1985 "parser.c"
 	{
 	if ( p == pe )
 		goto _test_eof;
@@ -2012,7 +2015,7 @@ case 1:
 cs = 0;
 	goto _out;
 tr2:
-#line 847 "parser.rl"
+#line 850 "parser.rl"
 	{
         char *np = JSON_parse_value(json, p, pe, &result, 0);
         if (np == NULL) { p--; {p++; cs = 10; goto _out;} } else {p = (( np))-1;}
@@ -2022,7 +2025,7 @@ cs = 0;
 	if ( ++p == pe )
 		goto _test_eof10;
 case 10:
-#line 2026 "parser.c"
+#line 2029 "parser.c"
 	switch( (*p) ) {
 		case 13: goto st10;
 		case 32: goto st10;
@@ -2111,7 +2114,7 @@ case 9:
 	_out: {}
 	}
 
-#line 875 "parser.rl"
+#line 878 "parser.rl"
 
     if (cs >= JSON_first_final && p == pe) {
         return result;
diff --git a/ext/json/ext/parser/parser.rl b/ext/json/ext/parser/parser.rl
index 6ebb2f6f..73f81341 100644
--- a/ext/json/ext/parser/parser.rl
+++ b/ext/json/ext/parser/parser.rl
@@ -689,6 +689,9 @@ static VALUE convert_encoding(VALUE source)
   }
 
  if (encindex == binary_encindex) {
+    // For historical reason, we silently reinterpret binary strings as UTF-8 if it would work.
+    // TODO: Deprecate in 2.8.0
+    // TODO: Remove in 3.0.0
     return rb_enc_associate_index(rb_str_dup(source), utf8_encindex);
   }
 
diff --git a/lib/json/pure/generator.rb b/lib/json/pure/generator.rb
index 2e38f6bc..517d4e27 100644
--- a/lib/json/pure/generator.rb
+++ b/lib/json/pure/generator.rb
@@ -339,6 +339,7 @@ def generate(obj)
           private def fast_serialize_string(string, buf) # :nodoc:
             buf << '"'
             string = string.encode(::Encoding::UTF_8) unless string.encoding == ::Encoding::UTF_8
+            raise GeneratorError, "source sequence is illegal/malformed utf-8" unless string.valid_encoding?
 
             if /["\\\x0-\x1f]/n.match?(string)
               buf << string.gsub(/["\\\x0-\x1f]/n, MAP)
diff --git a/test/json/json_generator_test.rb b/test/json/json_generator_test.rb
index 667baa03..7dc45e3a 100755
--- a/test/json/json_generator_test.rb
+++ b/test/json/json_generator_test.rb
@@ -443,6 +443,19 @@ def test_invalid_encoding_string
       "\x82\xAC\xEF".to_json
     end
     assert_includes error.message, "source sequence is illegal/malformed utf-8"
+
+    error = assert_raise(JSON::GeneratorError) do
+      JSON.dump("\x82\xAC\xEF")
+    end
+    assert_includes error.message, "source sequence is illegal/malformed utf-8"
+
+    assert_raise(Encoding::UndefinedConversionError) do
+      "\x82\xAC\xEF".b.to_json
+    end
+
+    assert_raise(Encoding::UndefinedConversionError) do
+      JSON.dump("\x82\xAC\xEF".b)
+    end
   end
 
   if defined?(JSON::Ext::Generator) and RUBY_PLATFORM != "java"