diff --git a/requirements.txt b/requirements.txt
index bc9550e..e4a0828 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
 # Build dependencies
 #python
 pytest
-pillow>=6.2.0
+pillow>=6.2.0,<10.0.0
 numpy>=1.16.4
 pandas>=0.24.2
 pyshp==2.1.0
@@ -15,4 +15,4 @@ mistune==0.8.4
 pyproj>=3.0.0
 geopandas
 matplotlib
-pyswmm>=1.2
\ No newline at end of file
+pyswmm>=1.2