diff --git a/.gitignore b/.gitignore
index 52cfc5793668d..cf11cd0ac20f9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -79,7 +79,6 @@ Makefile.fragments
 Makefile.objects
 
 # Directories for shared object files and headers generated by `./configure`
-include/
 libs/
 modules/
 
diff --git a/UPGRADING.INTERNALS b/UPGRADING.INTERNALS
index d393e66a4a0e5..3cbeb7af4d441 100644
--- a/UPGRADING.INTERNALS
+++ b/UPGRADING.INTERNALS
@@ -63,6 +63,7 @@ PHP 8.4 INTERNALS UPGRADE NOTES
    - Symbol DARWIN has been removed (use __APPLE__ to target Darwin systems).
    - Symbol MISSING_FCLOSE_DECL and M4 macro PHP_MISSING_FCLOSE_DECL removed.
    - Symbol HAVE_BSD_ICONV has been removed.
+   - M4 macro PHP_DEFINE (atomic includes) removed (use AC_DEFINE and config.h).
 
  c. Windows build system changes
    - The configure options --with-oci8-11g, --with-oci8-12c, --with-oci8-19 have
diff --git a/build/Makefile.global b/build/Makefile.global
index fe7d6a2cb0a51..8fa7ecb109de1 100644
--- a/build/Makefile.global
+++ b/build/Makefile.global
@@ -2,7 +2,7 @@ mkinstalldirs = $(top_srcdir)/build/shtool mkdir -p
 INSTALL = $(top_srcdir)/build/shtool install -c
 INSTALL_DATA = $(INSTALL) -m 644
 
-DEFS = -I$(top_builddir)/include -I$(top_builddir)/main -I$(top_srcdir)
+DEFS = -I$(top_builddir)/main -I$(top_srcdir)
 COMMON_FLAGS = $(DEFS) $(INCLUDES) $(EXTRA_INCLUDES) $(CPPFLAGS) $(PHP_FRAMEWORKPATH)
 
 all: $(all_targets)
@@ -135,7 +135,6 @@ distclean: clean
 	if test "$(srcdir)" != "$(builddir)"; then \
 	  rm -f ext/phar/phar/phar.inc; \
 	fi
-	$(EGREP) define'.*include/php' $(top_srcdir)/configure | $(SED) 's/.*>//'|xargs rm -f
 
 prof-gen:
 	CCACHE_DISABLE=1 $(MAKE) PROF_FLAGS=-fprofile-generate all
diff --git a/build/php.m4 b/build/php.m4
index a6707abed4506..e7f9e55a38018 100644
--- a/build/php.m4
+++ b/build/php.m4
@@ -69,15 +69,6 @@ AC_DEFUN([PHP_EXPAND_PATH],[
   fi
 ])
 
-dnl
-dnl PHP_DEFINE(WHAT [, value[, directory]])
-dnl
-dnl Creates builddir/include/what.h and in there #define WHAT value.
-dnl
-AC_DEFUN([PHP_DEFINE],[
-  [echo "#define ]$1[]ifelse([$2],,[ 1],[ $2])[" > ]ifelse([$3],,[include],[$3])[/php_]translit($1,A-Z,a-z)[.h]
-])
-
 dnl
 dnl PHP_SUBST(varname)
 dnl
@@ -135,12 +126,8 @@ dnl Creates build directories and Makefile placeholders.
 dnl
 AC_DEFUN([PHP_INIT_BUILD_SYSTEM],[
 AC_REQUIRE([PHP_CANONICAL_HOST_TARGET])dnl
-test -d include || $php_shtool mkdir include
 > Makefile.objects
 > Makefile.fragments
-dnl We need to play tricks here to avoid matching the grep line itself.
-pattern=define
-$EGREP $pattern'.*include/php' $srcdir/configure|$SED 's/.*>//'|xargs touch 2>/dev/null
 ])
 
 dnl
@@ -2115,9 +2102,7 @@ dnl PHP_CHECK_PDO_INCLUDES([found [, not-found]])
 dnl
 AC_DEFUN([PHP_CHECK_PDO_INCLUDES],[
   AC_CACHE_CHECK([for PDO includes], pdo_cv_inc_path, [
-    if test -f $abs_srcdir/include/php/ext/pdo/php_pdo_driver.h; then
-      pdo_cv_inc_path=$abs_srcdir/ext
-    elif test -f $abs_srcdir/ext/pdo/php_pdo_driver.h; then
+    if test -f $abs_srcdir/ext/pdo/php_pdo_driver.h; then
       pdo_cv_inc_path=$abs_srcdir/ext
     elif test -f $phpincludedir/ext/pdo/php_pdo_driver.h; then
       pdo_cv_inc_path=$phpincludedir/ext
diff --git a/configure.ac b/configure.ac
index 410c0168906b5..70334bf55ee06 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1692,7 +1692,7 @@ PHP_SUBST(all_targets)
 PHP_SUBST(install_targets)
 PHP_SUBST(install_binary_targets)
 
-PHP_INSTALL_HEADERS([Zend/ TSRM/ include/ main/ main/streams/])
+PHP_INSTALL_HEADERS([Zend/ TSRM/ main/ main/streams/])
 PHP_INSTALL_HEADERS([Zend/Optimizer], [ \
     zend_call_graph.h \
     zend_cfg.h \
diff --git a/docs/unix-build-system.md b/docs/unix-build-system.md
index 4df945a62b056..f1d0b45e344df 100644
--- a/docs/unix-build-system.md
+++ b/docs/unix-build-system.md
@@ -7,8 +7,6 @@
   especially noticeable on slower systems
 * slow recursive make replaced with one global Makefile
 * eases integration of proper dependencies
-* adds PHP_DEFINE(what[, value]) which creates a single include-file per what.
-  This will allow more fine-grained dependencies.
 * abandoning the "one library per directory" concept
 * improved integration of the CLI
 * several new targets: