diff -uNr a/gscm/README b/gscm/README
--- a/gscm/README 8720f7781977ed40fdd336e72f85d75bae99ee1cd913c358235d03671cf81e276ccc227904f7c601efb5e14547d122a07de7ecd26a58f85ccdc270ebac89a89b
+++ b/gscm/README 3011289ba281008dd6f314718348b5f2de6ebe54841ed89136c02273d322b69aad4e514d18bfdf13416dec27ddfa8ebb0525dcd04aace16a7d79cace0cd5410b
@@ -20,11 +20,11 @@
 1. Create the top-level /package directory if necessary and place the tree at its fully version-qualified path:
 
 	mkdir -p /package
-	cp -r /YOUR/PATH/TO/gscm /package/gscm-0.40.6
+	cp -r /YOUR/PATH/TO/gscm /package/gscm-0.40.7
 
 2. Run the install script from the above directory:
 
-	cd /package/gscm-0.40.6
+	cd /package/gscm-0.40.7
 	sh package/install
 
 3. Run the test suite if you like:
diff -uNr a/gscm/doc/CHANGES b/gscm/doc/CHANGES
--- a/gscm/doc/CHANGES cafdad5da765193b577cf00a3b6db06d690db1b48acad383330d2bbc6a3d4d215175083b1aa9f6230b633642527a5c4cde0f19b406390ceee355a2507c881505
+++ b/gscm/doc/CHANGES d251315af73a4670c7a857eb55909c7b6f7cd4e1f4af5529bdc2e1ff1b473c5e7e2078e712feb25699c03c7dc462dea966e1de9cfa1b7fcfb0292122d29c6655
@@ -776,3 +776,12 @@
 
 Documentation:
 - README moved from 'package' subdir to top level and massaged a bit.
+
+March 2023:
+
+40.maint7.
+
+Core:
+- Improve portability to glibc systems by defining the minimal required feature test macros and directly declaring some newer syscalls.
+- Add a HAVE_PIPE2 configurable, instead of commenting out the fallback code.
+- Expand related comments.
diff -uNr a/gscm/manifest b/gscm/manifest
--- a/gscm/manifest c872822ff26ad91e1140762a25c317e1be2fa8331e75ec85f979a1a254e81f356f13b463c61318edba685a8c932227c997537cd2f344539db1292d81f8f7b7b0
+++ b/gscm/manifest edb1d0e644b513e646ce663bb78f1ed64a4557e4a64e12632a4eaa5b6e17d9c24da7991e2b2b23b6f63a9797826e875d5b0c638796181d1af24c5f80586f5617
@@ -2,3 +2,4 @@
 648629 gscm_fix_m_whitespace_package_install jfw The -m argument to set heap memory allocation was broken; the control characters allowed as whitespace by the lexer were inconsistent; package installation was broken in the case of an existing version.
 654058 gscm_immutable_fill jfw The string-fill! and vector-fill! builtins failed to catch the errors of operating on immutable strings or vectors respectively.
 711740 gscm_usrbin jfw Change command symlink from /command/gscm to /usr/bin/gscm (see CHANGES for rationale) and update README.
+781987 gscm_glibc_build_fix jfw Improve portability to glibc systems and add a HAVE_PIPE2 configurable.
diff -uNr a/gscm/package/install b/gscm/package/install
--- a/gscm/package/install 38938de1d08dcfcb833b6adf3f35af18f37ea1283eb08e02b53d19f2952155374543d326215e076e5a14a00215727e3f854b8d4f7283442f47feb94472974d48
+++ b/gscm/package/install 2f0f4c18ba8498f8325a61aae566d521c12aa791b368a02d1c9a4e4d27e3d88a680e6242380810ba123878ecfcf84bcbe8f15832681d92b96821eb26256e2447
@@ -2,7 +2,7 @@
 set -e
 
 P=gscm
-V=0.40.6
+V=0.40.7
 cd /package/$P-$V
 
 # Versioned path duplicated in:
diff -uNr a/gscm/src/Makefile b/gscm/src/Makefile
--- a/gscm/src/Makefile 34dfec1e7baa7169fa4508ccfc9f277a803e50aa1b7bcece5719c9d75cdefb33a716cb8e2c68bf169dfc1a178516183cfc25bef7941462cebe0837ea45244266
+++ b/gscm/src/Makefile 6f71e198e552d8927c66a2c7c7f6cac5cb54973070575d7e85ba6177b679f62f18e0a5aee98108898b87bd9cc96bd1316f02280957688201815e9df04e812402
@@ -1,4 +1,4 @@
-PREFIX := /package/gscm-0.40.6
+PREFIX := /package/gscm-0.40.7
 ASM_ARCH := x86_64
 
 CFLAGS := -std=c99 -pedantic -Wall -Wextra -Winit-self -Wstrict-aliasing=1 -g -O2
diff -uNr a/gscm/src/gscm.c b/gscm/src/gscm.c
--- a/gscm/src/gscm.c 27041dc8a3fa1511bb10b6bd122fa21ae975857c5aba2e16081d74c6d0e9713bec0620677f61f2200230219591747e2d145f4a5e7b07935c7ecf71c4604e6b37
+++ b/gscm/src/gscm.c a1d87138bf0faaa75b4dfb9c9a03d1da9baa4ba4dc9daae671bfb4de2cf23dc3f8af08799af25e738f41ebcb248f74ec4b3e4f43a37d059ba22ec417c84ce8bc
@@ -5,9 +5,17 @@
  * artificial restrictions, and R5RS compliance with strict error checking.
  *
  * J. Welsh
- * January 2017 - April 2018
+ * January 2017 - March 2023
  */
 
+/* Define this if your system supports pipe2 and the O_CLOEXEC flag. Currently this is manually switched because I want to find out if there are any relevant systems that don't. (In other words - if you have to remove this to build, please let me know!) */
+#define HAVE_PIPE2
+
+/* make glibc define MAP_ANONYMOUS */
+#define _BSD_SOURCE
+/* make glibc 2.12+ define O_CLOEXEC */
+#define _POSIX_C_SOURCE 200809L
+
 #include <errno.h>
 #include <limits.h>
 #include <math.h>
@@ -27,14 +35,23 @@
 #define MAP_ANON MAP_ANONYMOUS
 #endif
 
+/* stdio.h dependencies listed explicitly */
 int snprintf(char *, size_t, const char *, ...); /* to be replaced */
+
+/* stdlib.h dependencies listed explicitly */
 void abort(void);
+
+/* string.h dependencies listed explicitly */
 size_t strlen(const char *);
 char *strerror(int);
 void *memcpy(void *, const void *, size_t);
 void *memset(void *, int, size_t);
 int memcmp(const void *, const void *, size_t);
+
+/* Newer syscalls which glibc is cranky about declaring: let's not play along with its feature test macro games more than strictly necessary. */
 pid_t vfork(void);
+int fdatasync(int);
+int pipe2(int[2], int);
 
 #include "gscm.h"
 
@@ -217,22 +234,26 @@
  */
 
 static int open_cloexec(const char *path, int flags) {
+#ifdef HAVE_PIPE2
 	return open(path, flags | O_CLOEXEC, 0666);
-	/* Non-atomic version for systems lacking O_CLOEXEC
+#else
+	/* Non-atomic version for systems lacking O_CLOEXEC. This doesn't currently matter, but if we go multi-threaded, we'll need locking for this and any exec family calls. And exec locking would be hard to enforce if this were linkable into larger programs. So basically there's a choice between portability or support for complexity. */
 	int fd = open(path, flags, 0666);
 	if (fd != -1) fcntl(fd, F_SETFD, FD_CLOEXEC);
 	return fd;
-	*/
+#endif
 }
 
 static int pipe_cloexec(int pipefd[2]) {
+#ifdef HAVE_PIPE2
 	return pipe2(pipefd, O_CLOEXEC);
-	/* Non-atomic version for systems lacking pipe2
+#else
+	/* Non-atomic version for systems lacking pipe2 (see O_CLOEXEC comments above). */
 	if (pipe(pipefd) == -1) return -1;
 	fcntl(pipefd[0], F_SETFD, FD_CLOEXEC);
 	fcntl(pipefd[1], F_SETFD, FD_CLOEXEC);
 	return 0;
-	*/
+#endif
 }
 
 /* Reliably catching close errors is NOT POSSIBLE on Linux and others. The call