diff --git a/src/share/poudriere/common.sh b/src/share/poudriere/common.sh
index ec92f82d..46842ccd 100755
--- a/src/share/poudriere/common.sh
+++ b/src/share/poudriere/common.sh
@@ -4209,6 +4209,7 @@ gather_distfiles() {
 	local from to
 	local sub dists d specials special origin
 	local dep_originspec pkgname flavor subpkg
+	local srcsize dstsize doinstall
 
 	from=$(realpath "$5")
 	to=$(realpath "$6")
@@ -4241,10 +4242,26 @@ gather_distfiles() {
 		if [ ! -f "${from}/${sub}/${d}" ]; then
 			continue
 		fi
-		# XXX: A --relative would be nice
-		install -pS -m 0644 "${from}/${sub}/${d}" \
-		    "${to}/${sub}/${d}" ||
-		    return 1
+		if [ ! -f "${to}/${sub}/${d}" ]; then
+			msg "GATHER_DISTFILES: missing ${to}/${sub}/${d}"
+			doinstall=1
+		else
+			dstsize=$(stat -f %z ${to}/${sub}/${d})
+			srcsize=$(stat -f %z ${from}/${sub}/${d})
+			if [ $srcsize -ne $dstsize ]; then
+				msg "GATHER_DISTFILES: size mismatch ($srcsize != $dstsize), overwriting ${to}/${sub}/${d}"
+				doinstall=1
+			else
+				msg "GATHER_DISTFILES: skipping copy ${to}/${sub}/${d}"
+				doinstall=0
+			fi
+		fi
+		if [ $doinstall -eq 1 ]; then
+			# XXX: A --relative would be nice
+			install -pS -m 0644 "${from}/${sub}/${d}" \
+			    "${to}/${sub}/${d}" ||
+			    return 1
+		fi
 	done
 
 	for special in ${specials}; do