diff --git a/tools/alias_collision/check_alias_collision.py b/tools/alias_collision/check_alias_collision.py
index effb126ec..9da18112d 100644
--- a/tools/alias_collision/check_alias_collision.py
+++ b/tools/alias_collision/check_alias_collision.py
@@ -12,6 +12,45 @@ ERROR_MESSAGE_TEMPLATE = (
     "Alias `%s` defined in `%s` already exists as alias `%s` in `%s`."
 )
 
+# TODO: We want that list to be empty
+KNOWN_COLLISIONS = [
+    "bcubc",
+    "pbl",
+    "gcd",
+    "h",
+    "brs",
+    "github",
+    "stackoverflow",
+    "zcl",
+    "afs",
+    "allpkgs",
+    "mydeb",
+    "jh",
+    "n",
+    "a",
+    "p",
+    "sf",
+    "sp",
+    "hs",
+    "db",
+    "rn",
+    "rs",
+    "ru",
+    "sc",
+    "sd",
+    "sd",
+    "sp",
+    "c",
+    "dr",
+    "rake",
+    "rubies",
+    "h",
+    "ma",
+    "map",
+    "mis",
+    "m",
+]
+
 
 def dir_path(path_string: str) -> Path:
     if Path(path_string).is_dir():
@@ -47,6 +86,9 @@ class Collision:
     existing_alias: Alias
     new_alias: Alias
 
+    def is_new_collision(self, known_collisions: List[str]) -> bool:
+        return self.new_alias.alias not in known_collisions
+
 
 def find_aliases_in_file(file: Path) -> List[Alias]:
     matches = re.findall(r"^alias (.*)='(.*)'", file.read_text(), re.M)
@@ -54,8 +96,7 @@ def find_aliases_in_file(file: Path) -> List[Alias]:
 
 
 def find_all_aliases(path: Path) -> list:
-    files = list(path.rglob("*.zsh"))
-    aliases = [find_aliases_in_file(file) for file in files]
+    aliases = [find_aliases_in_file(file) for file in path.rglob("*.zsh")]
     return list(itertools.chain(*aliases))
 
 
@@ -94,10 +135,13 @@ def main():
     args = parse_arguments()
     aliases = find_all_aliases(args.folder)
     collisions = check_for_duplicates(aliases)
-    print_collisions(collisions)
-    # TODO enable once all collisions are fixed
-    # if collisions:
-    #     exit(-1)
+    new_collisions = [
+        collision
+        for collision in collisions
+        if collision.is_new_collision(KNOWN_COLLISIONS)
+    ]
+    print_collisions(new_collisions)
+    return -1 if collisions else 0
 
 
 if __name__ == "__main__":
diff --git a/tools/alias_collision/tests/test_check_alias_collision.py b/tools/alias_collision/tests/test_check_alias_collision.py
index 5d7c28d2d..57ca17ed2 100644
--- a/tools/alias_collision/tests/test_check_alias_collision.py
+++ b/tools/alias_collision/tests/test_check_alias_collision.py
@@ -87,9 +87,7 @@ def test_find_aliases_in_file__one_conditional_alias_should_find_none(
     assert [] == result
 
 
-def test_check_for_duplicates__no_duplicates_should_return_empty_dict(
-    fs: FakeFilesystem,
-) -> None:
+def test_check_for_duplicates__no_duplicates_should_return_empty_dict() -> None:
     result = check_for_duplicates(
         [
             Alias("g", "git", Path("git.zsh")),
@@ -100,9 +98,7 @@ def test_check_for_duplicates__no_duplicates_should_return_empty_dict(
     assert result == []
 
 
-def test_check_for_duplicates__duplicates_should_have_one_collision(
-    fs: FakeFilesystem,
-) -> None:
+def test_check_for_duplicates__duplicates_should_have_one_collision() -> None:
     result = check_for_duplicates(
         [
             Alias("gc", "git commit", Path("git.zsh")),
@@ -115,3 +111,19 @@ def test_check_for_duplicates__duplicates_should_have_one_collision(
             Alias("gc", "git clone", Path("git.zsh")),
         )
     ]
+
+
+def test_is_new_collision__new_alias_not_in_known_collisions__should_return_true() -> (
+    None
+):
+    known_collisions = ["gc", "gd"]
+    new_alias = Alias("ga", "git add", Path("git.zsh"))
+    collision = Collision(Alias("gd", "git diff", Path("git.zsh")), new_alias)
+    assert collision.is_new_collision(known_collisions) is True
+
+
+def test_is_new_collision__new_alias_in_known_collisions__should_return_false() -> None:
+    known_collisions = ["gc", "gd", "ga"]
+    new_alias = Alias("ga", "git add", Path("git.zsh"))
+    collision = Collision(Alias("gd", "git diff", Path("git.zsh")), new_alias)
+    assert collision.is_new_collision(known_collisions) is False