diff --git a/src/include/compat/endian.h b/src/include/compat/endian.h
index 96b41d57..c0e988e2 100644
--- a/src/include/compat/endian.h
+++ b/src/include/compat/endian.h
@@ -20,10 +20,10 @@
 #define ENDIAN_H_COMPAT_SHIM
 #pragma once
 
-#if defined(HAVE_ENDIAN_H)
+#if __has_include_next(<endian.h>)
 #	pragma GCC system_header // Silence "warning: #include_next is a GCC extension"
 #	include_next <endian.h>
-#elif defined(HAVE_SYS_ENDIAN_H)
+#elif __has_include(<sys/endian.h>)
 #	include <sys/endian.h>
 #	if !defined(be16toh)
 #		define be16toh(x) betoh16(x)
diff --git a/src/include/compat/getopt.h b/src/include/compat/getopt.h
index ed2a87d6..be34d7ab 100644
--- a/src/include/compat/getopt.h
+++ b/src/include/compat/getopt.h
@@ -21,7 +21,7 @@
 #ifndef GETOPT_H_COMPAT_SHIM
 #define GETOPT_H_COMPAT_SHIM
 
-#if defined(HAVE_GETOPT_H)
+#if __has_include_next(<getopt.h>)
 #pragma GCC system_header // Silence "warning: #include_next is a GCC extension"
 #include_next <getopt.h>
 #else
diff --git a/src/include/compat/stdint.h b/src/include/compat/stdint.h
index 34c176e2..d3a25c6e 100644
--- a/src/include/compat/stdint.h
+++ b/src/include/compat/stdint.h
@@ -45,7 +45,7 @@
 
 #pragma GCC system_header // Silence "warning: #include_next is a GCC extension"
 
-#if defined(HAVE_STDINT_H) || !defined(HAVE_INTTYPES_H)
+#if __has_include(<stdint.h>) || !__has_include(<inttypes.h>)
 #include_next <stdint.h>
 #else
 #include_next <inttypes.h>
diff --git a/src/include/compat/unistd.h b/src/include/compat/unistd.h
index f5499f89..bd73997a 100644
--- a/src/include/compat/unistd.h
+++ b/src/include/compat/unistd.h
@@ -19,7 +19,7 @@
 #ifndef UNISTD_H_COMPAT_SHIM
 #define UNISTD_H_COMPAT_SHIM
 
-#if defined(HAVE_UNISTD_H)
+#if __has_include_next(<unistd.h>)
 #pragma GCC system_header // Silence "warning: #include_next is a GCC extension"
 #include_next <unistd.h>
 #endif
diff --git a/src/libespeak-ng/readclause.c b/src/libespeak-ng/readclause.c
index d287e028..dedf6c8b 100644
--- a/src/libespeak-ng/readclause.c
+++ b/src/libespeak-ng/readclause.c
@@ -38,7 +38,6 @@
 
 #include "readclause.h"
 #include "common.h"               // for GetFileLength, strncpy0
-#include "config.h"               // for HAVE_MKSTEMP
 #include "dictionary.h"           // for LookupDictList, DecodePhonemes, Set...
 #include "error.h"                // for create_file_error_context
 #include "phoneme.h"              // for phonSWITCH
diff --git a/src/libespeak-ng/speech.h b/src/libespeak-ng/speech.h
index 4d2f3684..ce039e89 100644
--- a/src/libespeak-ng/speech.h
+++ b/src/libespeak-ng/speech.h
@@ -31,7 +31,7 @@
 #endif
 
 #ifndef MAKE_MEM_UNDEFINED
-#  ifdef HAVE_VALGRIND_MEMCHECK_H
+#  if __has_include(<valgrind/memcheck.h>)
 #    include <valgrind/memcheck.h>
 #    define MAKE_MEM_UNDEFINED(addr, len) VALGRIND_MAKE_MEM_UNDEFINED(addr, len)
 #  else