diff --git a/bin/cp/cp.c b/bin/cp/cp.c
--- a/bin/cp/cp.c
+++ b/bin/cp/cp.c
@@ -179,9 +179,9 @@
 		target = dot;
 	} else if ((sep = strrchr(target, '/')) != NULL && sep[1] == '\0') {
 		have_trailing_slash = true;
-		while (sep > target + 1 && *(sep - 1) == '/')
+		while (sep > target && *sep == '/')
 			sep--;
-		*sep = '\0';
+		sep[1] = '\0';
 	}
 	/*
 	 * Copy target into to.base, leaving room for a possible separator
@@ -293,9 +293,11 @@
 		/*
 		 * We have previously made sure there is room for this.
 		 */
-		sep = strchr(to.base, '\0');
-		sep[0] = '/';
-		sep[1] = '\0';
+		if (strcmp(to.base, "/") != 0) {
+			sep = strchr(to.base, '\0');
+			sep[0] = '/';
+			sep[1] = '\0';
+		}
 	} else {
 		/*
 		 * We will create the destination directory imminently.
diff --git a/bin/cp/tests/cp_test.sh b/bin/cp/tests/cp_test.sh
--- a/bin/cp/tests/cp_test.sh
+++ b/bin/cp/tests/cp_test.sh
@@ -570,6 +570,27 @@
 	atf_check cmp dir/file dst/file
 }
 
+atf_test_case to_root cleanup
+to_root_head()
+{
+	atf_set "require.user" "root"
+}
+to_root_body()
+{
+	dst="$(atf_get ident).$$"
+	echo "$dst" >dst
+	echo "foo" >"$dst"
+	atf_check cp "$dst" /
+	atf_check cmp -s "$dst" "/$dst"
+	atf_check rm "/$dst"
+	atf_check cp "$dst" //
+	atf_check cmp -s "$dst" "/$dst"
+}
+to_root_cleanup()
+{
+	(dst=$(cat dst) && [ -n "/$dst" ] && [ -f "/$dst" ] && rm "/$dst") || true
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case basic
@@ -607,4 +628,5 @@
 	atf_add_test_case to_deaddirlink
 	atf_add_test_case to_link_outside
 	atf_add_test_case dstmode
+	atf_add_test_case to_root
 }