diff --git a/modules/mbedtls/configs/config-mbedtls.h b/modules/mbedtls/configs/config-mbedtls.h
index 38bf4fc63b9..d6d4f737aba 100644
--- a/modules/mbedtls/configs/config-mbedtls.h
+++ b/modules/mbedtls/configs/config-mbedtls.h
@@ -384,7 +384,7 @@
 #define MBEDTLS_PKCS1_V15
 #endif
 
-#if defined(CONFIG_MBEDTLS_PKCS1_V15)
+#if defined(CONFIG_MBEDTLS_PKCS1_V21)
 #define MBEDTLS_PKCS1_V21
 #endif