diff --git a/__tests__/integration/fixtures/error-include-path-site-name-contains-space/docs/index.md b/__tests__/integration/fixtures/ok-include-path-site-name-contains-space/docs/index.md
similarity index 100%
rename from __tests__/integration/fixtures/error-include-path-site-name-contains-space/docs/index.md
rename to __tests__/integration/fixtures/ok-include-path-site-name-contains-space/docs/index.md
diff --git a/__tests__/integration/fixtures/error-include-path-site-name-contains-space/mkdocs.yml b/__tests__/integration/fixtures/ok-include-path-site-name-contains-space/mkdocs.yml
similarity index 100%
rename from __tests__/integration/fixtures/error-include-path-site-name-contains-space/mkdocs.yml
rename to __tests__/integration/fixtures/ok-include-path-site-name-contains-space/mkdocs.yml
diff --git a/__tests__/integration/fixtures/error-include-path-site-name-contains-space/project-a/docs/README.md b/__tests__/integration/fixtures/ok-include-path-site-name-contains-space/project-a/docs/README.md
similarity index 100%
rename from __tests__/integration/fixtures/error-include-path-site-name-contains-space/project-a/docs/README.md
rename to __tests__/integration/fixtures/ok-include-path-site-name-contains-space/project-a/docs/README.md
diff --git a/__tests__/integration/fixtures/error-include-path-site-name-contains-space/project-a/mkdocs.yml b/__tests__/integration/fixtures/ok-include-path-site-name-contains-space/project-a/mkdocs.yml
similarity index 100%
rename from __tests__/integration/fixtures/error-include-path-site-name-contains-space/project-a/mkdocs.yml
rename to __tests__/integration/fixtures/ok-include-path-site-name-contains-space/project-a/mkdocs.yml
diff --git a/__tests__/integration/test.bats b/__tests__/integration/test.bats
index 4a5cd33..1a9d0a1 100644
--- a/__tests__/integration/test.bats
+++ b/__tests__/integration/test.bats
@@ -144,6 +144,11 @@ teardown() {
   [[ "$output" == *"This contains a sentence which only exists in the ok-mkdocs-git-revision-date-localized-plugin/project-a fixture."* ]]
 }
 
+@test "builds a mkdocs even if !include path has site_name containing spaces" {
+  cd ${fixturesDir}/ok-include-path-site-name-contains-space
+  assertSuccessMkdocs build
+}
+
 @test "fails if !include path is above current folder" {
   cd ${fixturesDir}/error-include-path-is-parent
   assertFailedMkdocs build
@@ -156,12 +161,6 @@ teardown() {
   [[ "$output" == *"[mkdocs-monorepo] We currently do not support nested !include statements inside of Mkdocs."* ]]
 }
 
-@test "fails if !include path has site_name containing spaces" {
-  cd ${fixturesDir}/error-include-path-site-name-contains-space
-  assertFailedMkdocs build
-  [[ "$output" == *"[mkdocs-monorepo] Site name can only contain letters, numbers, underscores, hyphens and forward-slashes. The regular expression we test against is '^[a-zA-Z0-9_\-/]+$'."* ]]
-}
-
 @test "fails if !include paths contains duplicate site_name values" {
   cd ${fixturesDir}/error-include-paths-duplicate-site-name
   assertFailedMkdocs build
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 652d448..dd555dd 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## 0.4.18
+
+- Allow inclusion of sub-docs `mkdocs.yml` even if its name isn't URL-friendly.
+  Works by slugifying non-URL friendly names. (#58)
+
 ## 0.4.17
 
 - Fixed bug where URLs in an included `mkdocs.yml` were prefixed by the `site_name` and thus did not support absolute URLs.
diff --git a/docs/limitations.md b/docs/limitations.md
index b53d44d..d347808 100644
--- a/docs/limitations.md
+++ b/docs/limitations.md
@@ -1,4 +1,3 @@
 # Caveats / Known Design Decisions
 
 - In an included `mkdocs.yml`, you cannot have `!include`. It is only supported in the root `mkdocs.yml`
-- In an included `mkdocs.yml`, your `site_name` must adhere follow the regular expression: `^[a-zA-Z0-9_\-/]+$`
diff --git a/mkdocs_monorepo_plugin/parser.py b/mkdocs_monorepo_plugin/parser.py
index 693f4fd..cae557f 100644
--- a/mkdocs_monorepo_plugin/parser.py
+++ b/mkdocs_monorepo_plugin/parser.py
@@ -17,6 +17,7 @@
 import copy
 import re
 
+from slugify import slugify
 from mkdocs.utils import yaml_load, warning_filter, dirname_to_title, get_markdown_title
 from urllib.parse import urlsplit
 log = logging.getLogger(__name__)
@@ -210,10 +211,7 @@ def getAlias(self):
         regex = '^[a-zA-Z0-9_\-/]+$'  # noqa: W605
 
         if re.match(regex, alias) is None:
-            log.critical(
-                "[mkdocs-monorepo] Site name can only contain letters, numbers, underscores, hyphens and forward-slashes. " +
-                "The regular expression we test against is '{}'.".format(regex))
-            raise SystemExit(1)
+            alias = slugify(self.navYaml["site_name"])
 
         return alias
 
diff --git a/requirements.txt b/requirements.txt
index f14d9d8..4136355 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ mkdocs>=1.1.1
 mkdocs-material>=5.1.0
 mkdocs-git-authors-plugin==0.3.2
 mkdocs-git-revision-date-localized-plugin==0.5.0
+python-slugify==4.0.1
diff --git a/setup.py b/setup.py
index 1cd881c..3bb365e 100644
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@
 
 setuptools.setup(
     name='mkdocs-monorepo-plugin',
-    version='0.4.17',
+    version='0.4.18',
     description='Plugin for adding monorepository support in Mkdocs.',
     long_description="""
         This introduces support for the !include syntax in mkdocs.yml, allowing you to import additional Mkdocs navigation.