diff --git a/dev_build.py b/dev_build.py
index b464424eb..303fb4275 100644
--- a/dev_build.py
+++ b/dev_build.py
@@ -81,7 +81,7 @@ def main():
     if not BUILD_DIR.exists():
         BUILD_DIR.mkdir()
 
-    tool_rebuild = f"cd {CWD / 'tool/microkit'} && cargo build --release"
+    tool_rebuild = f"cd {CWD / 'tool/microkit'} && cargo build"
     r = system(tool_rebuild)
     assert r == 0
 
@@ -90,7 +90,7 @@ def main():
     make_env["MICROKIT_BOARD"] = args.board
     make_env["MICROKIT_CONFIG"] = args.config
     make_env["MICROKIT_SDK"] = str(release)
-    make_env["MICROKIT_TOOL"] = (CWD / "target/release/microkit").absolute()
+    make_env["MICROKIT_TOOL"] = (CWD / "target/debug/microkit").absolute()
     make_env["LLVM"] = str(args.llvm)
 
     # Choose the makefile based on the `--example-from-sdk` command line flag
diff --git a/tool/microkit/src/sel4.rs b/tool/microkit/src/sel4.rs
index cb6db529d..641fa63c6 100644
--- a/tool/microkit/src/sel4.rs
+++ b/tool/microkit/src/sel4.rs
@@ -310,6 +310,7 @@ pub struct Config {
 }
 
 impl Config {
+    /// Refers to 'seL4_UserTop'
     pub fn user_top(&self) -> u64 {
         match self.arch {
             Arch::Aarch64 => match self.hypervisor {
@@ -325,16 +326,17 @@ impl Config {
         }
     }
 
+    /// Refers to the 'PPTR_BASE' define in kernel source
     pub fn virtual_base(&self) -> u64 {
         match self.arch {
             Arch::Aarch64 => match self.hypervisor {
                 true => 0x0000008000000000,
-                false => u64::pow(2, 64) - u64::pow(2, 39),
+                false => 0xffffff8000000000,
             },
             Arch::Riscv64 => match self.riscv_pt_levels.unwrap() {
-                RiscvVirtualMemory::Sv39 => u64::pow(2, 64) - u64::pow(2, 38),
+                RiscvVirtualMemory::Sv39 => 0xffffffc000000000,
             },
-            Arch::X86_64 => u64::pow(2, 64) - u64::pow(2, 39),
+            Arch::X86_64 => 0xffffff8000000000,
         }
     }