diff --git a/pkgs/development/compilers/gambit/bootstrap.nix b/pkgs/development/compilers/gambit/bootstrap.nix
index f00a8b6efc91..2fb9e3ce2fc4 100644
--- a/pkgs/development/compilers/gambit/bootstrap.nix
+++ b/pkgs/development/compilers/gambit/bootstrap.nix
@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, autoconf, ... }:
+{ stdenv, fetchurl, autoconf, gcc, coreutils, ... }:
 
 stdenv.mkDerivation {
   pname = "gambit-bootstrap";
@@ -12,6 +12,10 @@ stdenv.mkDerivation {
   buildInputs = [ autoconf ];
 
   configurePhase = ''
+    export CC=${gcc}/bin/gcc CXX=${gcc}/bin/g++ \
+           CPP=${gcc}/bin/cpp CXXCPP=${gcc}/bin/cpp LD=${gcc}/bin/ld \
+           XMKMF=${coreutils}/bin/false
+    unset CFLAGS LDFLAGS LIBS CPPFLAGS CXXFLAGS
     ./configure --prefix=$out
   '';
 
diff --git a/pkgs/development/compilers/gambit/build.nix b/pkgs/development/compilers/gambit/build.nix
index 7a3324d75602..e17241b6d98d 100644
--- a/pkgs/development/compilers/gambit/build.nix
+++ b/pkgs/development/compilers/gambit/build.nix
@@ -1,4 +1,19 @@
-{ stdenv, git, openssl, autoconf, pkgs, makeStaticLibraries, version, src }:
+{ stdenv, git, openssl, autoconf, pkgs, makeStaticLibraries, version, gcc, src, coreutils }:
+
+# Note that according to a benchmark run by Marc Feeley on May 2018,
+# clang is 10x (with default settings) to 15% (with -O2) slower than GCC at compiling
+# Gambit output, producing code that is 3x slower. IIRC the benchmarks from Gambit@30,
+# the numbers were still heavily in favor of GCC in October 2019.
+# Thus we use GCC over clang, even on macOS.
+
+# Also note that I (fare) just ran benchmarks from https://github.com/ecraven/r7rs-benchmarks
+# with Gambit 4.9.3 with -O1 vs -O2 vs -Os on Feb 2020. Which wins depends on the benchmark.
+# The fight is unclear between -O1 and -O2, where -O1 wins more often, by up to 17%,
+# but sometimes -O2 wins, once by up to 43%, so that overall -O2 is 5% faster.
+# However, -Os seems more consistent in winning slightly against both -O1 and -O2,
+# and is overall 15% faster than -O2. As for compile times, -O1 is fastest,
+# -Os is about 29%-33% slower than -O1, while -O2 is about 40%-50% slower than -O1.
+# Overall, -Os seems like the best choice, and that's what we now use.
 
 stdenv.mkDerivation rec {
   pname = "gambit";
@@ -7,38 +22,48 @@ stdenv.mkDerivation rec {
 
   bootstrap = import ./bootstrap.nix ( pkgs );
 
-  # Use makeStaticLibraries to enable creation of statically linked binaries
-  buildInputs = [ git autoconf bootstrap openssl (makeStaticLibraries openssl)];
+  # TODO: if/when we can get all the library packages we depend on to have static versions,
+  # we could use something like (makeStaticLibraries openssl) to enable creation
+  # of statically linked binaries by gsc.
+  buildInputs = [ git autoconf bootstrap openssl ];
+
+  configureFlags = [
+    "--enable-single-host"
+    "--enable-c-opt=-Os"
+    "--enable-gcc-opts"
+    "--enable-shared"
+    "--enable-absolute-shared-libs" # Yes, NixOS will want an absolute path, and fix it.
+    "--enable-poll"
+    "--enable-openssl"
+    "--enable-default-runtime-options=f8,-8,t8" # Default to UTF-8 for source and all I/O
+    # "--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"
+    # "--enable-track-scheme"
+    # "--enable-high-res-timing"
+    # "--enable-max-processors=4"
+    # "--enable-multiple-vms"
+    # "--enable-dynamic-tls"
+    # "--enable-multiple-threaded-vms"  # when SMP branch is merged in
+    # "--enable-thread-system=posix"    # default when --enable-multiple-vms is on.
+    # "--enable-profile"
+    # "--enable-coverage"
+    # "--enable-inline-jumps"
+    # "--enable-char-size=1" # default is 4
+  ];
 
   configurePhase = ''
-    options=(
-      --prefix=$out
-      --enable-single-host
-      --enable-c-opt=-O2
-      --enable-gcc-opts
-      --enable-shared
-      --enable-absolute-shared-libs # Yes, NixOS will want an absolute path, and fix it.
-      --enable-poll
-      --enable-openssl
-      --enable-default-runtime-options="f8,-8,t8" # Default to UTF-8 for source and all I/O
-      #--enable-debug # Nope: enables plenty of good stuff, but also the costly console.log
+    export CC=${gcc}/bin/gcc CXX=${gcc}/bin/g++ \
+           CPP=${gcc}/bin/cpp CXXCPP=${gcc}/bin/cpp LD=${gcc}/bin/ld \
+           XMKMF=${coreutils}/bin/false
+    unset CFLAGS LDFLAGS LIBS CPPFLAGS CXXFLAGS
+    ./configure --prefix=$out ${builtins.concatStringsSep " " configureFlags}
 
-      #--enable-multiple-versions # Nope, NixOS already does version multiplexing
-      #--enable-guide
-      #--enable-track-scheme
-      #--enable-high-res-timing
-      #--enable-max-processors=4
-      #--enable-multiple-vms
-      #--enable-dynamic-tls
-      #--enable-multiple-vms
-      #--enable-multiple-threaded-vms  ## when SMP branch is merged in
-      #--enable-thread-system=posix    ## default when --enable-multiple-vms is on.
-      #--enable-profile
-      #--enable-coverage
-      #--enable-inline-jumps
-      #--enable-char-size=1" ; default is 4
-    )
-    ./configure ''${options[@]}
+    # OS-specific paths are hardcoded in ./configure
+    substituteInPlace config.status \
+      --replace /usr/local/opt/openssl/lib "${openssl.out}/lib" \
+      --replace /usr/local/opt/openssl@1.1/lib "${openssl.out}/lib"
+    ./config.status
   '';
 
   buildPhase = ''
diff --git a/pkgs/development/compilers/gambit/unstable.nix b/pkgs/development/compilers/gambit/unstable.nix
index d855b83f0afc..4c33c83c67b1 100644
--- a/pkgs/development/compilers/gambit/unstable.nix
+++ b/pkgs/development/compilers/gambit/unstable.nix
@@ -1,13 +1,13 @@
 { stdenv, callPackage, fetchFromGitHub }:
 
 callPackage ./build.nix {
-  version = "unstable-2019-07-21";
-# git-version = "4.9.3-109-g3b5f74fa";
+  version = "unstable-2020-02-24";
+# git-version = "4.9.3-979-gc69e9f70";
   src = fetchFromGitHub {
     owner = "feeley";
     repo = "gambit";
-    rev = "3b5f74fae74b2159e3bf6923f29a18b31cc15dcc";
-    sha256 = "07cb0d8754dqhxawkp5dp4y0bsa9kfald4dkj60j5yfnsp81y5mi";
+    rev = "c69e9f70dfdc6545353b135a5d5e2f9234f1e1cc";
+    sha256 = "1f69n7yzzdv3wpnjlrbck38xpa8115vbady43mc544l39ckklr0k";
   };
   inherit stdenv;
 }
diff --git a/pkgs/development/compilers/gerbil/build.nix b/pkgs/development/compilers/gerbil/build.nix
index e2ab09764827..21c2936fa0f8 100644
--- a/pkgs/development/compilers/gerbil/build.nix
+++ b/pkgs/development/compilers/gerbil/build.nix
@@ -3,9 +3,6 @@
   openssl, zlib, sqlite, libxml2, libyaml, libmysqlclient, lmdb, leveldb, postgresql,
   version, git-version, gambit, src }:
 
-# TODO: distinct packages for gerbil-release and gerbil-devel
-# TODO: make static compilation work
-
 stdenv.mkDerivation rec {
   pname = "gerbil";
   inherit version;
@@ -32,19 +29,23 @@ stdenv.mkDerivation rec {
       substituteInPlace "$f" --replace '"gsc"' '"${gambit}/bin/gsc"'
     done
     substituteInPlace "etc/gerbil.el" --replace '"gxc"' "\"$out/bin/gxc\""
+'';
 
-    cat > etc/gerbil_static_libraries.sh <<EOF
-#OPENSSL_LIBCRYPTO=${makeStaticLibraries openssl}/lib/libcrypto.a # MISSING!
-#OPENSSL_LIBSSL=${makeStaticLibraries openssl}/lib/libssl.a # MISSING!
-ZLIB=${makeStaticLibraries zlib}/lib/libz.a
+## TODO: make static compilation work.
+## For that, get all the packages below to somehow expose static libraries,
+## so we can offer users the option to statically link them into Gambit and/or Gerbil.
+## Then add the following to the postPatch script above:
+#     cat > etc/gerbil_static_libraries.sh <<EOF
+# OPENSSL_LIBCRYPTO=${makeStaticLibraries openssl}/lib/libcrypto.a # MISSING!
+# OPENSSL_LIBSSL=${makeStaticLibraries openssl}/lib/libssl.a # MISSING!
+# ZLIB=${makeStaticLibraries zlib}/lib/libz.a
 # SQLITE=${makeStaticLibraries sqlite}/lib/sqlite.a # MISSING!
 # LIBXML2=${makeStaticLibraries libxml2}/lib/libxml2.a # MISSING!
 # YAML=${makeStaticLibraries libyaml}/lib/libyaml.a # MISSING!
-MYSQL=${makeStaticLibraries libmysqlclient}/lib/mariadb/libmariadb.a
+# MYSQL=${makeStaticLibraries libmysqlclient}/lib/mariadb/libmariadb.a
 # LMDB=${makeStaticLibraries lmdb}/lib/mysql/libmysqlclient_r.a # MISSING!
-LEVELDB=${makeStaticLibraries lmdb}/lib/libleveldb.a
-EOF
-  '';
+# LEVELDB=${makeStaticLibraries leveldb}/lib/libleveldb.a
+# EOF
 
   buildPhase = ''
     runHook preBuild
@@ -52,6 +53,14 @@ EOF
     # Enable all optional libraries
     substituteInPlace "src/std/build-features.ss" --replace '#f' '#t'
 
+    # Enable autodetection of a default GERBIL_HOME
+    for i in src/gerbil/boot/gx-init-exe.scm src/gerbil/boot/gx-init.scm ; do
+      substituteInPlace "$i" --replace '(getenv "GERBIL_HOME" #f)' "(getenv \"GERBIL_HOME\" \"$out\")"
+    done
+    for i in src/gerbil/boot/gxi-init.scm src/gerbil/compiler/driver.ss src/gerbil/runtime/gx-gambc.scm src/std/build.ss src/tools/build.ss ; do
+      substituteInPlace "$i" --replace '(getenv "GERBIL_HOME")' "(getenv \"GERBIL_HOME\" \"$out\")"
+    done
+
     # gxprof testing uses $HOME/.cache/gerbil/gxc
     export HOME=$$PWD
 
@@ -71,7 +80,7 @@ EOF
 export GERBIL_HOME=$out
 case "\$1" in -:*) GSIOPTIONS=\$1 ; shift ;; esac
 if [[ \$# = 0 ]] ; then
-  exec ${gambit}/bin/gsi \$GSIOPTIONS \$GERBIL_HOME/lib/gxi-init \$GERBIL_HOME/lib/gxi-interactive - ;
+  exec ${gambit}/bin/gsi \$GSIOPTIONS \$GERBIL_HOME/lib/gxi-init \$GERBIL_HOME/lib/gxi-interactive -
 else
   exec ${gambit}/bin/gsi \$GSIOPTIONS \$GERBIL_HOME/lib/gxi-init "\$@"
 fi
@@ -85,8 +94,8 @@ EOF
     description = "Gerbil Scheme";
     homepage    = "https://github.com/vyzo/gerbil";
     license     = stdenv.lib.licenses.lgpl2;
-    # NB regarding platforms: only actually tested on Linux, *should* work everywhere,
-    # but *might* need adaptation e.g. on macOS. Please report success and/or failure to fare.
+    # NB regarding platforms: regularly tested on Linux, only occasionally on macOS.
+    # Please report success and/or failure to fare.
     platforms   = stdenv.lib.platforms.unix;
     maintainers = with stdenv.lib.maintainers; [ fare ];
   };
diff --git a/pkgs/development/compilers/gerbil/unstable.nix b/pkgs/development/compilers/gerbil/unstable.nix
index 5f0347aa9a66..eb78eed35ee9 100644
--- a/pkgs/development/compilers/gerbil/unstable.nix
+++ b/pkgs/development/compilers/gerbil/unstable.nix
@@ -1,15 +1,15 @@
 { stdenv, callPackage, fetchFromGitHub, gambit, gambit-unstable }:
 
 callPackage ./build.nix {
-  version = "unstable-2019-11-15";
-  git-version = "0.15.1-461-gee22de62";
+  version = "unstable-2020-02-27";
+  git-version = "0.16-DEV-493-g1ffb74db";
   #gambit = gambit-unstable;
   gambit = gambit;
   src = fetchFromGitHub {
     owner = "vyzo";
     repo = "gerbil";
-    rev = "ee22de628a656ee59c6c72bc25d7b2e25a4ece2f";
-    sha256 = "1n1j596b91k9xcmv22l72nga6wv20bka2q51ik2jw2vkcw8zkc1c";
+    rev = "1ffb74db5ffd49b4bad751586cef5e619c891d41";
+    sha256 = "1szmdp8lvy5gpcwn5bpa7x383m6vywl35xa7hz9a5vs1rq4w2097";
   };
   inherit stdenv;
 }