diff --git a/papermill/tests/test_translators.py b/papermill/tests/test_translators.py
index 0edc1f07..a14f5099 100644
--- a/papermill/tests/test_translators.py
+++ b/papermill/tests/test_translators.py
@@ -107,6 +107,9 @@ def test_translate_comment_python(test_input, expected):
                 Parameter("b", "float", "-2.3432", "My b variable"),
             ],
         ),
+        # Regression test for #864: '=' inside string literals shouldn't trip parsing.
+        ('s = "a=b"', [Parameter("s", "None", '"a=b"', "")]),
+        ("s = 'a=b'", [Parameter("s", "None", "'a=b'", "")]),
     ],
 )
 def test_inspect_python(test_input, expected):
diff --git a/papermill/translators.py b/papermill/translators.py
index 1cb43d89..6c2466a6 100644
--- a/papermill/translators.py
+++ b/papermill/translators.py
@@ -1,7 +1,9 @@
+import io
 import logging
 import math
 import re
 import shlex
+import tokenize
 
 from .exceptions import PapermillException
 from .models import Parameter
@@ -9,6 +11,21 @@
 logger = logging.getLogger(__name__)
 
 
+def _count_assignment_operators(line):
+    """Count top-level assignment operators in a Python source line.
+
+    Uses ``tokenize`` so that ``=`` characters appearing inside string
+    literals (e.g. ``s = "a=b"``) are not counted as assignment
+    operators. Falls back to a naive ``line.count('=')`` if tokenization
+    fails (e.g. for incomplete multiline definitions).
+    """
+    try:
+        tokens = tokenize.tokenize(io.BytesIO(line.encode("utf-8")).readline)
+        return sum(1 for tok in tokens if tok.type == tokenize.OP and tok.string == "=")
+    except (tokenize.TokenError, SyntaxError):
+        return line.count("=")
+
+
 class PapermillTranslators:
     '''
     The holder which houses any translator registered with the system.
@@ -242,7 +259,7 @@ def flatten_accumulator(accumulator):
             if len(line.strip()) == 0 or line.strip().startswith('#'):
                 continue  # Skip blank and comment
 
-            nequal = line.count("=")
+            nequal = _count_assignment_operators(line)
             if nequal > 0:
                 grouped_variable.append(flatten_accumulator(accumulator))
                 accumulator = []