diff --git a/lib/clang/llvm.build.mk b/lib/clang/llvm.build.mk
index 239c74ceedf..f0e8081e8fc 100644
--- a/lib/clang/llvm.build.mk
+++ b/lib/clang/llvm.build.mk
@@ -22,7 +22,9 @@ CFLAGS+=	-D__STDC_CONSTANT_MACROS
 CFLAGS+=	-D__STDC_FORMAT_MACROS
 CFLAGS+=	-D__STDC_LIMIT_MACROS
 CFLAGS+=	-DHAVE_VCS_VERSION_INC
-#CFLAGS+=	-DNDEBUG
+.if ${MK_LLVM_ASSERTIONS} == "no"
+CFLAGS+=	-DNDEBUG
+.endif
 
 TARGET_ARCH?=	${MACHINE_ARCH}
 BUILD_ARCH?=	${MACHINE_ARCH}
diff --git a/share/mk/src.opts.mk b/share/mk/src.opts.mk
index 08cc821df0e..0e569287547 100644
--- a/share/mk/src.opts.mk
+++ b/share/mk/src.opts.mk
@@ -132,6 +132,7 @@ __DEFAULT_YES_OPTIONS = \
     LLD \
     LLD_BOOTSTRAP \
     LLD_IS_LD \
+    LLVM_ASSERTIONS \
     LLVM_COV \
     LLVM_TARGET_ALL \
     LOADER_GELI \
diff --git a/tools/build/options/WITHOUT_LLVM_ASSERTIONS b/tools/build/options/WITHOUT_LLVM_ASSERTIONS
new file mode 100644
index 00000000000..73d39e55322
--- /dev/null
+++ b/tools/build/options/WITHOUT_LLVM_ASSERTIONS
@@ -0,0 +1,2 @@
+.\" $FreeBSD$
+Set to disable debugging assertions in LLVM.
diff --git a/tools/build/options/WITH_LLVM_ASSERTIONS b/tools/build/options/WITH_LLVM_ASSERTIONS
new file mode 100644
index 00000000000..32cf014b583
--- /dev/null
+++ b/tools/build/options/WITH_LLVM_ASSERTIONS
@@ -0,0 +1,2 @@
+.\" $FreeBSD$
+Set to enable debugging assertions in LLVM.