diff --git a/requirements.txt b/requirements.txt
index 6c6567ff7c4dbb60603630e298fbc5a1d9bc441f..ad856ae7c3ff0a6120f2b0d7aee6009402d472ac 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,11 +6,11 @@
 
 
 # Python SDL2 library dependencies.
-pysdl2
-pysdl2-dll
+PySDL2~=0.9.9
+pysdl2-dll~=2.0.16
 
 # System font-parsing dependencies.
-fclist
+fclist~=1.1.1
 
 # Graph datastructure library.
-networkx
+networkx~=2.6.3