diff --git a/pkgs/development/compilers/gambit/bootstrap.nix b/pkgs/development/compilers/gambit/bootstrap.nix
index a29f45a4e7a5..753938e95aa3 100644
--- a/pkgs/development/compilers/gambit/bootstrap.nix
+++ b/pkgs/development/compilers/gambit/bootstrap.nix
@@ -6,11 +6,11 @@
 
 gccStdenv.mkDerivation {
   pname = "gambit-bootstrap";
-  version = "4.9.3";
+  version = "4.9.5";
 
   src = fetchurl {
-    url = "http://www.iro.umontreal.ca/~gambit/download/gambit/v4.9/source/gambit-v4_9_3.tgz";
-    sha256 = "1p6172vhcrlpjgia6hsks1w4fl8rdyjf9xjh14wxfkv7dnx8a5hk";
+    url = "https://gambitscheme.org/4.9.5/gambit-v4_9_5.tgz";
+    sha256 = "sha256-4o74218OexFZcgwVAFPcq498TK4fDlyDiUR5cHP4wdw=";
   };
 
   buildInputs = [ autoconf ];
diff --git a/pkgs/development/compilers/gambit/build.nix b/pkgs/development/compilers/gambit/build.nix
index 029225629154..e06c05b1f244 100644
--- a/pkgs/development/compilers/gambit/build.nix
+++ b/pkgs/development/compilers/gambit/build.nix
@@ -39,11 +39,14 @@ gccStdenv.mkDerivation rec {
     "--enable-targets=${gambit-params.targets}"
     "--enable-single-host"
     "--enable-c-opt=${optimizationSetting}"
+    "--enable-c-opt-rts=-O2"
     "--enable-gcc-opts"
     "--enable-shared"
     "--enable-absolute-shared-libs" # Yes, NixOS will want an absolute path, and fix it.
     "--enable-openssl"
+    #"--enable-default-compile-options='(compactness 9)'" # Make life easier on the JS backend
     "--enable-default-runtime-options=${gambit-params.defaultRuntimeOptions}"
+    # "--enable-rtlib-debug" # used by Geiser, but only on recent-enough gambit, and messes js runtime
     # "--enable-debug" # Nope: enables plenty of good stuff, but also the costly console.log
     # "--enable-multiple-versions" # Nope, NixOS already does version multiplexing
     # "--enable-guide"
@@ -84,18 +87,19 @@ gccStdenv.mkDerivation rec {
   '';
 
   buildPhase = ''
-    # Make bootstrap compiler, from release bootstrap
+    echo "Make bootstrap compiler, from release bootstrap"
     mkdir -p boot
     cp -rp ${bootstrap}/gambit/. boot/.
     chmod -R u+w boot
     cd boot
     cp ../gsc/makefile.in ../gsc/*.scm gsc/
+    echo > include/stamp.h # No stamp needed for the bootstrap compiler
     ./configure
     for i in lib gsi gsc ; do (cd $i ; make -j$NIX_BUILD_CORES) ; done
     cd ..
     cp boot/gsc/gsc gsc-boot
 
-    # Now use the bootstrap compiler to build the real thing!
+    echo "Now use the bootstrap compiler to build the real thing!"
     make -j$NIX_BUILD_CORES from-scratch
     ${lib.optionalString gambit-params.modules "make -j$NIX_BUILD_CORES modules"}
   '';
@@ -107,6 +111,7 @@ gccStdenv.mkDerivation rec {
   '';
 
   doCheck = true;
+  dontStrip = true;
 
   meta = gambit-support.meta;
 }
diff --git a/pkgs/development/compilers/gambit/default.nix b/pkgs/development/compilers/gambit/default.nix
index 8f77daa4173b..cb4f5f9501ca 100644
--- a/pkgs/development/compilers/gambit/default.nix
+++ b/pkgs/development/compilers/gambit/default.nix
@@ -1,10 +1,10 @@
 { callPackage, fetchurl }:
 
 callPackage ./build.nix rec {
-  version = "4.9.3";
+  version = "4.9.5";
   git-version = version;
   src = fetchurl {
-    url = "http://www.iro.umontreal.ca/~gambit/download/gambit/v4.9/source/gambit-v4_9_3.tgz";
-    sha256 = "1p6172vhcrlpjgia6hsks1w4fl8rdyjf9xjh14wxfkv7dnx8a5hk";
+    url = "https://gambitscheme.org/4.9.5/gambit-v4_9_5.tgz";
+    sha256 = "sha256-4o74218OexFZcgwVAFPcq498TK4fDlyDiUR5cHP4wdw=";
   };
 }
diff --git a/pkgs/development/compilers/gambit/gambit-support.nix b/pkgs/development/compilers/gambit/gambit-support.nix
index be745367ec03..13827b4a59c7 100644
--- a/pkgs/development/compilers/gambit/gambit-support.nix
+++ b/pkgs/development/compilers/gambit/gambit-support.nix
@@ -3,24 +3,25 @@
 rec {
   stable-params = {
     stable = true;
-    defaultRuntimeOptions = "f8,-8,t8";
-    buildRuntimeOptions = "f8,-8,t8";
-    fix-stamp = git-version : "";
-    targets = "java,js,php,python,ruby";
-    modules = false;
-  };
-
-  unstable-params = {
-    stable = false;
     defaultRuntimeOptions = "iL,fL,-L,tL";
     buildRuntimeOptions = "i8,f8,-8,t8";
-    fix-stamp = git-version : ''
+    targets = "js"; # arm,java,js,php,python,riscv-32,riscv-64,ruby,x86,x86-64
+    #fixStamp = _: _: _: "";
+    fixStamp = git-version: stampYmd: stampHms: ''
+      echo "Fixing timestamp recipe in Makefile"
       substituteInPlace configure \
         --replace "$(grep '^PACKAGE_VERSION=.*$' configure)" 'PACKAGE_VERSION="v${git-version}"' \
         --replace "$(grep '^PACKAGE_STRING=.*$' configure)" 'PACKAGE_STRING="Gambit v${git-version}"' ;
+      substituteInPlace include/makefile.in \
+                --replace "echo > stamp.h;" "(echo '#define ___STAMP_VERSION \"${git-version}\"'; echo '#define ___STAMP_YMD ${toString stampYmd}'; echo '#define ___STAMP_HMS ${toString stampHms}';) > stamp.h;";
     '';
-    targets = "arm,java,js,php,python,riscv-32,riscv-64,ruby,x86,x86-64"; # eats 100% cpu on _digest
-    modules = false;
+    modules = true;
+    extraOptions = [];
+  };
+
+  unstable-params = stable-params // {
+    stable = false;
+    extraOptions = ["--enable-trust-c-tco"];
   };
 
   export-gambopt = params : "export GAMBOPT=${params.buildRuntimeOptions} ;";