diff --git a/doc/manual/R-exts.texi b/doc/manual/R-exts.texi
index 72f0619ecb..075d1c9128 100644
--- a/doc/manual/R-exts.texi
+++ b/doc/manual/R-exts.texi
@@ -5894,14 +5894,17 @@ standards and the @code{<tr1/@var{name}>} headers are not supplied by some of
 the compilers used for @R{}, including on macOS.  (Use the C++11
 versions instead.)
 
-@c Centos had 10 years of support, for Centos 7 expiring in June 2024.
 @c RHEL has 10 years, with more extended support, up to 4 years.
 @c Ubuntu LTS has 5 years' general support and 8 extended support.
 @c Ubuntu 16.04 (EOL 2021-04) came with GCC 5.4 but 7 was available
 @c Ubuntu 18.04 came with GCC 7.3 or 7.4.
-@c RHEL/Centos 6 came with GCC 4.4.
-@c RHEL/Centos 7 came with GCC 4.8, with 4.4 available.
-@c RHEL/Centos 8 has GCC 8.
+@c Ubuntu 20.04 came with GCC 9.4
+@c Ubuntu 22.04 came with GCC 11
+@c RHEL 6 came with GCC 4.4.
+@c RHEL 7 came with GCC 4.8, with 4.4 available.
+@c RHEL 8 has GCC 8 with 9 available
+@c RHEL 9 has GCC 11
+@c All versions of Cwntos is now EOL.
 A common error is to assume recent versions of compilers or OSes.  In
 production environments `long term support' versions of OSes may be in
 use for many years,@footnote{Ubuntu provides 5 years of support (but
diff --git a/src/include/R_ext/Boolean.h b/src/include/R_ext/Boolean.h
index 56bce4e4a0..19a315aab5 100644
--- a/src/include/R_ext/Boolean.h
+++ b/src/include/R_ext/Boolean.h
@@ -1,6 +1,6 @@
 /*
  *  R : A Computer Language for Statistical Data Analysis
- *  Copyright (C) 2000, 2001 The R Core Team.
+ *  Copyright (C) 2000, 2025 The R Core Team.
  *
  *  This header file is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU Lesser General Public License as published by
@@ -29,13 +29,22 @@
 #undef FALSE
 #undef TRUE
 
-#ifdef  __cplusplus
+// Fer now, only when the compiler claims to be a C23 compiler.
+
+#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
+typedef bool Rboolean;
+# define FALSE false
+# define TRUE true
+# define _R_RBOOLEAN_IS_BOOL_ 1
+#else
+#  ifdef  __cplusplus
 extern "C" {
-#endif
+# endif
 typedef enum { FALSE = 0, TRUE /*, MAYBE */ } Rboolean;
 
-#ifdef  __cplusplus
+# ifdef  __cplusplus
 }
+# endif
 #endif
 
 #endif /* R_EXT_BOOLEAN_H_ */
diff --git a/src/include/R_ext/RStartup.h b/src/include/R_ext/RStartup.h
index fb7a8aa264..2165477cbc 100644
--- a/src/include/R_ext/RStartup.h
+++ b/src/include/R_ext/RStartup.h
@@ -73,7 +73,8 @@ typedef struct
     R_SIZE_T max_vsize;
     R_SIZE_T max_nsize;
     R_SIZE_T ppsize;
-    Rboolean NoRenviron : 16;
+    // This used to be Rboolean, but that is not guaraneteed to have >= 16 bits
+    int NoRenviron : 16;
 	/* RstartVersion has been added in R 4.2.0. Earlier, NoRenviron was an
 	   int (normally 32-bit like Rboolean), so on most machines the
 	   version would become 0 when setting NoRenviron to FALSE in