diff --git a/mk/config.mk b/mk/config.mk
index 9e29295..4df9fc3 100644
--- a/mk/config.mk
+++ b/mk/config.mk
@@ -23,7 +23,7 @@ else
 FILESYSTEM_CONFIG?=config/$(ARCH)/$(BOARD)/$(CONFIG_NAME).toml
 endif
 ## Filesystem size in MB (default comes from filesystem_size in the FILESYSTEM_CONFIG)
-FILESYSTEM_SIZE?=$(shell grep filesystem_size $(FILESYSTEM_CONFIG) | cut -d' ' -f3)
+FILESYSTEM_SIZE?=$(shell cargo run --release --manifest-path installer/Cargo.toml -- --filesystem-size -c $(FILESYSTEM_CONFIG))
 ## Flags to pass to redoxfs-mkfs. Add --encrypt to set up disk encryption
 REDOXFS_MKFS_FLAGS?=
 ## Set to 1 to enable Podman build, any other value will disable it