diff --git a/compose.yaml b/compose.yaml
index 47a78ee..01f6e18 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -200,7 +200,7 @@ services:
 
   mergepdf:
     <<: *common
-    image: islandora/mergepdf:6.3.19
+    image: islandora/mergepdf:6.3.19@sha256:69f391d2058463f815c87b6703a39e38f5e61bf27b15b305ebf4bda64268110c
     secrets:
       - source: CERT_PUBLIC_KEY
       - source: CERT_AUTHORITY