diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -95,7 +95,6 @@
 CWARNFLAGS.clang+=	-Wno-error=unused-but-set-variable
 .endif
 .if ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} >= 150000
-CWARNFLAGS.clang+=	-Wno-error=deprecated-non-prototype
 CWARNFLAGS.clang+=	-Wno-error=unused-but-set-parameter
 .endif
 .endif # WARNS <= 6
diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -47,10 +47,9 @@
 CWARNEXTRA+=	-Wno-error=shift-negative-value
 CWARNEXTRA+=	-Wno-address-of-packed-member
 .if ${COMPILER_VERSION} >= 150000
-# Clang 15 has much more aggressive diagnostics about K&R prototypes,
-# mismatched prototypes, and unused-but-set variables. Make these
+# Clang 15 has much more aggressive diagnostics about
+# mismatched prototypes and unused-but-set variables. Make these
 # non-fatal for the time being.
-CWARNEXTRA+=	-Wno-error=deprecated-non-prototype
 CWARNEXTRA+=	-Wno-error=strict-prototypes
 CWARNEXTRA+=	-Wno-error=unused-but-set-variable
 .endif