diff --git a/pkgs/development/libraries/science/chemistry/mctc-lib/default.nix b/pkgs/development/libraries/science/chemistry/mctc-lib/default.nix
index e9be83970fbf..aeb7c8bb6f56 100644
--- a/pkgs/development/libraries/science/chemistry/mctc-lib/default.nix
+++ b/pkgs/development/libraries/science/chemistry/mctc-lib/default.nix
@@ -24,7 +24,7 @@ stdenv.mkDerivation rec {
 
   postInstall = ''
     substituteInPlace $out/lib/pkgconfig/${pname}.pc \
-      --replace "''${prefix}" ""
+      --replace "''${prefix}/" ""
   '';
 
   doCheck = true;