diff --git a/mk/prefix.mk b/mk/prefix.mk
index 001c5f4d9..c9d085bdd 100644
--- a/mk/prefix.mk
+++ b/mk/prefix.mk
@@ -10,7 +10,7 @@ BINUTILS_BRANCH=redox-2.43.1
 GCC_BRANCH=redox-13.2.0
 LIBTOOL_VERSION=2.5.4
 # official RISC-V support introduced in newer version
-UPSTREAM_RUSTC_VERSION="2025-11-15"
+UPSTREAM_RUSTC_VERSION=2025-11-15
 
 export PREFIX_RUSTFLAGS=-L $(ROOT)/$(PREFIX_INSTALL)/$(TARGET)/lib
 export RUSTUP_TOOLCHAIN=$(ROOT)/$(PREFIX_INSTALL)