diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index ca008677..946f1443 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -55,6 +55,11 @@ jobs:
       matrix:
         python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
         numpy-version: ["1.0", "2.0"]
+        sly-version: ["0.5"]
+        include:
+          - python-version: "3.11"
+            numpy-version: "2.0"
+            sly-version: "0.4"
     
     steps:
       - uses: actions/checkout@v4
@@ -64,8 +69,9 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - run: pip install numpy~=${{ matrix.numpy-version }}
         name: install specific numpy version
-      - run: pip install --user . montepy[test]
-      - run: pip install --user . montepy[build]
+      - run: pip install sly~=${{ matrix.sly-version }}
+        name: install specific sly version
+      - run: pip install --user . montepy[test,build]
       - run: pip uninstall -y pytest-profiling
         name: Uninstall incompatible library
         if: ${{ matrix.python-version == '3.13' }}
diff --git a/pyproject.toml b/pyproject.toml
index 6afab82b..0a5ca915 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,7 +35,7 @@ classifiers = [
 ]
 dependencies = [
 	"numpy>=1.18",
-	"sly==0.5"
+	"sly>= 0.4, <=0.5"
 ]
 
 [project.optional-dependencies]