diff --git a/configure.ac b/configure.ac
index 4ac7264ab4..53f67d50f8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -142,6 +142,13 @@ TEST_CFLAGS="-Wno-vla"
 # the compiler has a different built-in setting)
 STD_CPPFLAGS="-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2"
 
+#
+# Define constexpr if it is missing from the compiler
+#
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[constexpr int foo = 0;]])],
+		  [],
+		  [AC_DEFINE([constexpr],[static const],[Define compatibility shim for non-C23 compilers.])])
+
 #
 # Additional compiler settings.
 #
diff --git a/lib/isc/include/isc/attributes.h b/lib/isc/include/isc/attributes.h
index 4ed540f5a8..eb1bb53e2e 100644
--- a/lib/isc/include/isc/attributes.h
+++ b/lib/isc/include/isc/attributes.h
@@ -102,9 +102,3 @@
 #else
 #define ISC_ATTR_UNUSED __attribute__((__unused__))
 #endif
-
-#if __STDC_VERSION__ >= 202311L
-#define ISC_CONSTEXPR constexpr
-#else
-#define ISC_CONSTEXPR static const
-#endif
diff --git a/lib/isc/include/isc/time.h b/lib/isc/include/isc/time.h
index 0ba40129fa..9fa025c9f4 100644
--- a/lib/isc/include/isc/time.h
+++ b/lib/isc/include/isc/time.h
@@ -18,18 +18,17 @@
 #include <inttypes.h>
 #include <time.h>
 
-#include <isc/attributes.h>
 #include <isc/types.h>
 
 /*
  * Define various time conversion constants.
  */
-ISC_CONSTEXPR unsigned int MS_PER_SEC = 1000;
-ISC_CONSTEXPR unsigned int US_PER_MS = 1000;
-ISC_CONSTEXPR unsigned int NS_PER_US = 1000;
-ISC_CONSTEXPR unsigned int US_PER_SEC = 1000 * 1000;
-ISC_CONSTEXPR unsigned int NS_PER_MS = 1000 * 1000;
-ISC_CONSTEXPR unsigned int NS_PER_SEC = 1000 * 1000 * 1000;
+constexpr unsigned int MS_PER_SEC = 1000;
+constexpr unsigned int US_PER_MS = 1000;
+constexpr unsigned int NS_PER_US = 1000;
+constexpr unsigned int US_PER_SEC = 1000 * 1000;
+constexpr unsigned int NS_PER_MS = 1000 * 1000;
+constexpr unsigned int NS_PER_SEC = 1000 * 1000 * 1000;
 
 /*
  * ISC_FORMATHTTPTIMESTAMP_SIZE needs to be 30 in C locale and potentially