diff --git a/Makefile.inc1 b/Makefile.inc1
index 8b3d3147bb97..c883d14d0b5a 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -524,9 +524,9 @@ PACKAGE=	kernel
 #
 
 BOOTSTRAPPING?=	0
-# Keep these in sync -- see below for special case exception
-MINIMUM_SUPPORTED_OSREL?= 900044
-MINIMUM_SUPPORTED_REL?= 9.1
+# Keep these in sync
+MINIMUM_SUPPORTED_OSREL?= 1002501
+MINIMUM_SUPPORTED_REL?= 10.3
 
 # Common environment for world related stages
 CROSSENV+=	\
@@ -1845,18 +1845,6 @@ _elftoolchain_libs= lib/libelf lib/libdwarf
 .endif
 
 legacy: .PHONY
-# Temporary special case for automatically detecting the clang compiler issue
-# Note: 9.x didn't have FreeBSD_version bumps often enough, so you may need to
-# set BOOTSTRAPPING to 0 if you're stable/9 tree post-dates r286035 but is before
-# the version bump in r296219 (from July 29, 2015 -> Feb 29, 2016).
-.if ${BOOTSTRAPPING} != 0 && \
-	${WANT_COMPILER_TYPE} == "clang" && ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} < 30601
-.if   ${BOOTSTRAPPING} > 1000000 && ${BOOTSTRAPPING} < 1002501
-	@echo "ERROR: Source upgrades from stable/10 prior to r286033 are not supported."; false
-.elif ${BOOTSTRAPPING} >  900000 && ${BOOTSTRAPPING} <  903509
-	@echo "ERROR: Source upgrades from stable/9 prior to r286035 are not supported."; false
-.endif
-.endif
 .if ${BOOTSTRAPPING} < ${MINIMUM_SUPPORTED_OSREL} && ${BOOTSTRAPPING} != 0
 	@echo "ERROR: Source upgrades from versions prior to ${MINIMUM_SUPPORTED_REL} are not supported."; \
 	false