diff --git a/metadata/fields/custom/license.py b/metadata/fields/custom/license.py
index f70b2d21d..5661e92af 100644
--- a/metadata/fields/custom/license.py
+++ b/metadata/fields/custom/license.py
@@ -11,6 +11,9 @@ from typing import List, Tuple, Optional
 _THIS_DIR = os.path.abspath(os.path.dirname(__file__))
 # The repo's root directory.
 _ROOT_DIR = os.path.abspath(os.path.join(_THIS_DIR, "..", "..", ".."))
+# Bad delimiter characters.
+BAD_DELIMITERS = ["/", ";", " and ", " or "]
+BAD_DELIMITERS_REGEX = re.compile("|".join(re.escape(delimiter) for delimiter in BAD_DELIMITERS))
 
 # Add the repo's root directory for clearer imports.
 sys.path.insert(0, _ROOT_DIR)
@@ -92,6 +95,15 @@ class LicenseField(field_types.SingleLineTextField):
       if util.is_empty(license):
         return vr.ValidationError(
                     reason=f"{self._name} has an empty value.")
+      if BAD_DELIMITERS_REGEX.search(license):
+        return vr.ValidationError(
+                reason=f"{self._name} contains a bad license separator. "
+                "Separate licenses by commas only.",
+                # Try and preemptively address the root cause of this behaviour,
+                # which is having multiple choices for a license.
+                additional=[f"When given a choice of licenses, chose the most "
+                            "permissive one, do not list all options."]
+        )
       if not allowed:
         not_allowlisted.append(license)
 
diff --git a/metadata/tests/fields_test.py b/metadata/tests/fields_test.py
index 78a8ff323..30f449309 100644
--- a/metadata/tests/fields_test.py
+++ b/metadata/tests/fields_test.py
@@ -123,10 +123,17 @@ class FieldValidationTest(unittest.TestCase):
                 "APSL-2.0, MIT",
                 "APSL-2.0 ,MIT",
             ],
-            error_values=["", "\n", ",", "Apache 2.0 ,"],
+            error_values=[
+                "",
+                "\n",
+                ",",
+                "Apache 2.0 ,",
+                "Custom / MIT",
+                "Apache-2.0 and MIT",
+                "Apache-2.0; MIT; BSD-2-Clause",
+            ],
             warning_values=[
                 "Custom license",
-                "Custom / MIT",
                 "Custom, MIT",
             ],
         )