diff --git a/pyhocon/converter.py b/pyhocon/converter.py
index 158437f..bb93e5c 100644
--- a/pyhocon/converter.py
+++ b/pyhocon/converter.py
@@ -115,7 +115,10 @@ def to_hocon(cls, config, compact=False, indent=2, level=0):
                 lines += '\n'.join(bet_lines)
                 lines += '\n{indent}]'.format(indent=''.rjust((level - 1) * indent, ' '))
         elif isinstance(config, str):
-            if '\n' in config and len(config) > 1:
+            # A triple-quoted literal cannot contain the `"""` sequence (it
+            # would terminate the literal early), so such strings must use the
+            # escaped single-quoted form instead.
+            if '\n' in config and len(config) > 1 and '"""' not in config:
                 lines = '"""{value}"""'.format(value=config)  # multilines
             else:
                 lines = '"{value}"'.format(value=cls._escape_string(config))
@@ -127,7 +130,7 @@ def to_hocon(cls, config, compact=False, indent=2, level=0):
                 lines += '?'
             lines += config.variable + '}' + config.ws
         elif isinstance(config, ConfigQuotedString):
-            if '\n' in config.value and len(config.value) > 1:
+            if '\n' in config.value and len(config.value) > 1 and '"""' not in config.value:
                 lines = '"""{value}"""'.format(value=config.value)  # multilines
             else:
                 lines = '"{value}"'.format(value=cls._escape_string(config.value))
diff --git a/tests/test_converter.py b/tests/test_converter.py
index d4d80b0..f991393 100644
--- a/tests/test_converter.py
+++ b/tests/test_converter.py
@@ -1,7 +1,7 @@
 # -*- encoding: utf-8 -*-
 from datetime import timedelta
 
-from pyhocon import ConfigTree
+from pyhocon import ConfigFactory, ConfigTree
 from pyhocon.converter import HOCONConverter
 
 
@@ -108,6 +108,16 @@ def test_format_multiline_string(self):
         assert 'a = """b\n"""' == to_hocon({'a': 'b\n'})
         assert 'a = """\n\n"""' == to_hocon({'a': '\n\n'})
 
+    def test_format_multiline_string_with_triple_quote(self):
+        # A multiline string that itself contains `"""` cannot use the
+        # triple-quoted form (the embedded `"""` would terminate the literal
+        # early), so it must fall back to the escaped single-quoted form and
+        # still round-trip.
+        assert r'a = "a\nb\"\"\"c"' == to_hocon({'a': 'a\nb"""c'})
+        for value in ('a\nb"""c', 'before\n"""middle"""\nafter', '"""\nleading'):
+            parsed = ConfigFactory.parse_string(to_hocon({'a': value}))['a']
+            assert parsed == value
+
     def test_format_time_delta(self):
         for time_delta, expected_result in ((timedelta(days=0), 'td = 0 seconds'),
                                             (timedelta(days=5), 'td = 5 days'),