diff --git a/repo2docker/utils.py b/repo2docker/utils.py
index 10347198..d9d48dfc 100644
--- a/repo2docker/utils.py
+++ b/repo2docker/utils.py
@@ -473,14 +473,29 @@ def is_local_pip_requirement(line):
     # we just care that this isn't a "local pip requirement"
     if line.startswith("--pre"):
         return False
+
     # strip off things like `--editable=`. Long form arguments require a =
     if line.startswith("--"):
-        line = line.split("=", 1)[1]
+        # if splitting doesn't work it is probably because the line contains
+        # a syntax error or our "parser" is too simplistic so we return True
+        # just in case
+        try:
+            line = line.split("=", 1)[1]
+        except IndexError:
+            return True
+
     # strip off short form arguments like `-e`. Short form arguments can be
     # followed by a space `-e foo` or use `-e=foo`. The latter is not handled
     # here. We can deal with it when we see someone using it.
     if line.startswith("-"):
-        line = line.split(None, 1)[1]
+        # if splitting doesn't work it is probably because the line contains
+        # a syntax error or our "parser" is too simplistic so we return True
+        # just in case
+        try:
+            line = line.split(None, 1)[1]
+        except IndexError:
+            return True
+
     if "file://" in line:
         # file references break isolation
         return True
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 7b45ffff..38b8beb6 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -147,7 +147,13 @@ def test_open_guess_encoding():
         ("numpy", False),
         ("# -e .", False),
         ("--pre", False),
+        # pip ignores the package name and treats this like `--pre` on a line
+        # by itself
         ("--pre pandas", False),
+        # These are invalid lines as far as pip is concerned, check that our
+        # code is robust and continues running
+        ("--unrecognized", True),
+        ("-e", True),
     ],
 )
 def test_local_pip_requirement(req, is_local):