diff --git a/ChangeLog b/ChangeLog
index 2351f847ef..b85c7c6e6e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2025-05-19  Collin Funk  <collin.funk1@gmail.com>
 
+	stdckdint-h: Work around missing declarations with g++ 15.0.
+	* modules/stdckdint-h (configure.ac): Generate the header if the system
+	has one and C++ is being used.
+
 	stdckdint-h C++ tests: Verify the ckd_* functions can be invoked.
 	* tests/test-stdckdint-h-c++.cc (main): Invoke ckd_add, ckd_sub, and
 	ckd_mul.
diff --git a/modules/stdckdint-h b/modules/stdckdint-h
index 24e26cfb69..ff777d8d62 100644
--- a/modules/stdckdint-h
+++ b/modules/stdckdint-h
@@ -12,7 +12,11 @@ bool
 configure.ac:
 AC_CHECK_HEADERS_ONCE([stdckdint.h])
 if test $ac_cv_header_stdckdint_h = yes; then
-  GL_GENERATE_STDCKDINT_H=false
+  if test -n "$CXX" && test "$CXX" != no; then
+    GL_GENERATE_STDCKDINT_H=true
+  else
+    GL_GENERATE_STDCKDINT_H=false
+  fi
 else
   GL_GENERATE_STDCKDINT_H=true
 fi