diff --git a/UPDATING b/UPDATING
--- a/UPDATING
+++ b/UPDATING
@@ -27,6 +27,13 @@
 	world, or to merely disable the most expensive debugging functionality
 	at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+202508xx:
+	The CLEAN option has been switched back from default-on to default-off.
+	This reverts the 20250808 change below, which had reverted the 20240729
+	change before it.  Note that some src.conf(5) options are known to break
+	ABI or compatibility in ways that may require a clean build initially
+	when switched.
+
 20250813:
 	Commit cce64f2e6851 changed the internal KAPI between the NFS
 	modules.  As such, all of them need to be rebuilt from sources.
diff --git a/share/man/man5/src.conf.5 b/share/man/man5/src.conf.5
--- a/share/man/man5/src.conf.5
+++ b/share/man/man5/src.conf.5
@@ -1,5 +1,5 @@
 .\" DO NOT EDIT-- this file is @generated by tools/build/options/makeman.
-.Dd August 8, 2025
+.Dd August 15, 2025
 .Dt SRC.CONF 5
 .Os
 .Sh NAME
@@ -411,8 +411,8 @@
 .It Va WITHOUT_CLANG_FULL
 Avoid building the ARCMigrate, Rewriter and StaticAnalyzer components of
 the Clang C/C++ compiler.
-.It Va WITHOUT_CLEAN
-Do not clean before building world and/or kernel.
+.It Va WITH_CLEAN
+Clean before building world and/or kernel.
 .It Va WITHOUT_CPP
 Do not build
 .Xr cpp 1 .
diff --git a/share/mk/src.opts.mk b/share/mk/src.opts.mk
--- a/share/mk/src.opts.mk
+++ b/share/mk/src.opts.mk
@@ -80,7 +80,6 @@
     CDDL \
     CLANG \
     CLANG_BOOTSTRAP \
-    CLEAN \
     CPP \
     CROSS_COMPILER \
     CRYPT \
@@ -201,6 +200,7 @@
     BHYVE_SNAPSHOT \
     CLANG_EXTRAS \
     CLANG_FORMAT \
+    CLEAN \
     DIALOG \
     DETECT_TZ_CHANGES \
     DISK_IMAGE_TOOLS_BOOTSTRAP \
diff --git a/tools/build/options/WITH_CLEAN b/tools/build/options/WITH_CLEAN
new file mode 100644
--- /dev/null
+++ b/tools/build/options/WITH_CLEAN
@@ -0,0 +1 @@
+Clean before building world and/or kernel.