diff --git a/stand/defs.mk b/stand/defs.mk
index 2f8d97ae0f2c..e446fd0f6c94 100644
--- a/stand/defs.mk
+++ b/stand/defs.mk
@@ -53,7 +53,12 @@ CFLAGS+=	-I${SASRC} -D_STANDALONE
 CFLAGS+=	-I${SYSDIR}
 # Spike the floating point interfaces
 CFLAGS+=	-Ddouble=jagged-little-pill -Dfloat=floaty-mcfloatface
-
+# Slim down the image. This saves about 15% in size with clang 6 on x86
+# Our most constrained /boot/loader env is BIOS booting on x86, where
+# our text + data + BTX have to fit into 640k below the ISA hole.
+# Experience has shown that problems arise between ~520k to ~530k.
+CFLAGS.clang+=	-Oz
+CFLAGS.gcc+=	-Os
 
 # GELI Support, with backward compat hooks (mostly)
 .if defined(LOADER_NO_GELI_SUPPORT)