diff --git a/ch04/requirements.txt b/ch04/requirements.txt
index 0d84467..c95bd03 100644
--- a/ch04/requirements.txt
+++ b/ch04/requirements.txt
@@ -2,5 +2,5 @@ keras==2.1.2
 tensorflow==1.8.0
 h5py==2.7.1
 matplotlib==2.1.1
-PIllow==5.1.0
+PIllow==9.0.0
 pandas==0.22.0
diff --git a/ch04/requirements_gpu.txt b/ch04/requirements_gpu.txt
index f8b1a7f..b7b90f1 100644
--- a/ch04/requirements_gpu.txt
+++ b/ch04/requirements_gpu.txt
@@ -2,5 +2,5 @@ keras==2.1.2
 tensorflow-gpu==1.8.0
 h5py==2.7.1
 matplotlib==2.1.1
-PIllow==5.1.0
+PIllow==9.0.0
 pandas==0.22.0