diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,6 @@
+2025-09-07
+        * Version bump (4.5.1). (#666)
+
 2025-07-07
         * Version bump (4.5). (#642)
 
diff --git a/copilot-libraries.cabal b/copilot-libraries.cabal
--- a/copilot-libraries.cabal
+++ b/copilot-libraries.cabal
@@ -1,6 +1,6 @@
 cabal-version:       >=1.10
 name:                copilot-libraries
-version:             4.5
+version:             4.5.1
 synopsis:            Libraries for the Copilot language.
 description:
   Libraries for the Copilot language.
@@ -38,10 +38,10 @@
 
   build-depends: base             >= 4.9 && < 5
 
-               , containers       >= 0.4 && < 0.8
-               , mtl              >= 2.0 && < 2.4
-               , parsec           >= 2.0 && < 3.2
-               , copilot-language >= 4.5 && < 4.6
+               , containers       >= 0.4   && < 0.8
+               , mtl              >= 2.0   && < 2.4
+               , parsec           >= 2.0   && < 3.2
+               , copilot-language >= 4.5.1 && < 4.6
 
   exposed-modules:
       Copilot.Library.Libraries