diff --git a/Makefile b/Makefile
index 503434d2a..f733eed8f 100644
--- a/Makefile
+++ b/Makefile
@@ -111,7 +111,7 @@ endif
 
 PKG_CONFIG ?= pkg-config
 SED ?= sed
-BISON ?= bison -k
+BISON ?= bison
 STRIP ?= strip
 AWK ?= awk
 
diff --git a/flake.nix b/flake.nix
index 00ad7d865..19ba59f17 100644
--- a/flake.nix
+++ b/flake.nix
@@ -41,7 +41,7 @@
         packages.default = yosys;
         defaultPackage = yosys;
         devShell = pkgs.mkShell {
-          buildInputs = with pkgs; [ clang llvmPackages.bintools gcc bison flex libffi tcl readline python3 zlib git gtest abc-verifier verilog boost python3Packages.boost valgrind ];
+          buildInputs = with pkgs; [ clang llvmPackages.bintools gcc bison flex libffi tcl readline python3 zlib git gtest abc-verifier verilog boost python3Packages.boost ];
         };
       }
     );