diff --git a/datagateway_api/src/common/config.py b/datagateway_api/src/common/config.py
index f713c211..40cfe6ea 100644
--- a/datagateway_api/src/common/config.py
+++ b/datagateway_api/src/common/config.py
@@ -27,10 +27,11 @@ def validate_extension(extension):
     """
     extension = extension.strip()
 
-    if not extension.startswith("/"):
-        raise ValueError("must start with '/'")
-    if extension.endswith("/"):
-        raise ValueError("must not end with '/'")
+    if extension:
+        if not extension.startswith("/"):
+            raise ValueError("must start with '/'")
+        if extension.endswith("/") and len(extension) != 1:
+            raise ValueError("must not end with '/'")
 
     return extension
 
diff --git a/test/test_config.py b/test/test_config.py
index 86c52750..8b01bbbc 100644
--- a/test/test_config.py
+++ b/test/test_config.py
@@ -3,7 +3,7 @@
 
 import pytest
 
-from datagateway_api.src.common.config import APIConfig
+from datagateway_api.src.common.config import APIConfig, validate_extension
 
 
 @pytest.fixture()
@@ -103,3 +103,39 @@ def test_set_backend_type(self, test_config):
         test_config.datagateway_api.set_backend_type("backend_name_changed")
 
         assert test_config.datagateway_api.backend == "backend_name_changed"
+
+    @pytest.mark.parametrize(
+        "input_extension, expected_extension",
+        [
+            pytest.param("/", "/", id="Slash"),
+            pytest.param("", "", id="Empty string, implied slash"),
+            pytest.param("/datagateway-api", "/datagateway-api", id="DataGateway API"),
+            pytest.param(
+                "   /datagateway-api   ",
+                "/datagateway-api",
+                id="DataGateway API with trailing and leading spaces",
+            ),
+            pytest.param("/search-api", "/search-api", id="Search API"),
+            pytest.param(
+                "   /search-api   ",
+                "/search-api",
+                id="Search API with trailing and leading spaces",
+            ),
+        ],
+    )
+    def test_valid_extension_validation(self, input_extension, expected_extension):
+        test_extension = validate_extension(input_extension)
+
+        assert test_extension == expected_extension
+
+    @pytest.mark.parametrize(
+        "input_extension",
+        [
+            pytest.param("datagateway-api", id="DataGateway API with no leading slash"),
+            pytest.param("search-api", id="Search API with no leading slash"),
+            pytest.param("/my-extension/", id="Extension with trailing slash"),
+        ],
+    )
+    def test_invalid_extension_validation(self, input_extension):
+        with pytest.raises(ValueError):
+            validate_extension(input_extension)