diff --git a/chip/stm32/config-stm32f100.h b/chip/stm32/config-stm32f100.h
index 750465a250..552aa7ac58 100644
--- a/chip/stm32/config-stm32f100.h
+++ b/chip/stm32/config-stm32f100.h
@@ -27,7 +27,11 @@
 #define CONFIG_SECTION_A_OFF    CONFIG_FW_A_OFF
 #define CONFIG_SECTION_A_SIZE   CONFIG_FW_A_SIZE
 #define CONFIG_SECTION_B_OFF    CONFIG_FW_B_OFF
+#ifdef CONFIG_NO_RW_B
+#define CONFIG_SECTION_B_SIZE   0
+#else /* CONFIG_NO_RW_B */
 #define CONFIG_SECTION_B_SIZE   CONFIG_FW_B_SIZE
+#endif /* CONFIG_NO_RW_B */
 
 /* no keys for now */
 #define CONFIG_VBOOT_ROOTKEY_OFF    (CONFIG_FW_RO_OFF + CONFIG_FW_RO_SIZE)