diff --git a/requirements.txt b/requirements.txt
index 9de4fdd16c636a9ba0531ae1807ccc57a7826ffe..3e315492fb2b1fce9b8d5e1af853e59877d12dd7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,3 +5,4 @@ pandas~=1.2.3
 julian~=0.14
 astropy~=5.1
 tqdm~=4.59.0
+GalSim~=2.4.5