diff --git a/keyboards/handwired/onekey/blackpill_f401/blackpill_f401.c b/keyboards/handwired/onekey/blackpill_f401/blackpill_f401.c
new file mode 100644
index 0000000000..956932329c
--- /dev/null
+++ b/keyboards/handwired/onekey/blackpill_f401/blackpill_f401.c
@@ -0,0 +1,23 @@
+/* Copyright 2020 Sergey Vlasov (sigprof)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include QMK_KEYBOARD_H
+
+void board_init(void) {
+    // B9 is configured as I2C1_SDA in the board file; that function must be
+    // disabled before using B7 as I2C1_SDA.
+    setPinInputHigh(B9);
+}