diff --git a/apps/rust-hello/build.rs b/apps/rust-hello/build.rs
index 7883f81..4e50d21 100644
--- a/apps/rust-hello/build.rs
+++ b/apps/rust-hello/build.rs
@@ -6,7 +6,7 @@ fn main() {
     println!("cargo:rustc-link-arg-bin=rust-hello=-T../common/linker.ld");
 
     let bindings = bindgen::Builder::default()
-        .header("../../common/uvm32_sys.h")
+        .header("uvm32_headers.h")
         .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
         .generate()
         .expect("Unable to generate bindings");
diff --git a/apps/rust-hello/uvm32_headers.h b/apps/rust-hello/uvm32_headers.h
new file mode 100644
index 0000000..ed6218e
--- /dev/null
+++ b/apps/rust-hello/uvm32_headers.h
@@ -0,0 +1,2 @@
+#include "../../common/uvm32_sys.h"
+#include "../../common/uvm32_common_custom.h"
diff --git a/common/uvm32_common_custom.h b/common/uvm32_common_custom.h
index 82bb6f4..6739938 100644
--- a/common/uvm32_common_custom.h
+++ b/common/uvm32_common_custom.h
@@ -1,4 +1,5 @@
-// Definitions needed by both host and target
+// Syscall definitions needed by both host and target for sample apps
+// These are not required when building a custom host target code with uvm32
 
 // syscalls for exposed host functions, start at 0
 #define UVM32_SYSCALL_PUTC      0x00000000
diff --git a/common/uvm32_sys.h b/common/uvm32_sys.h
index 0829864..7caa737 100644
--- a/common/uvm32_sys.h
+++ b/common/uvm32_sys.h
@@ -1,8 +1,15 @@
+#ifndef UVM32_SYS_H
+#define UVM32_SYS_H 1
+
+// Common definitions used by both uvm32.c and any code running inside VM
+
 // System provided UVM32_SYSCALLs, start at 0x10000000
 #define UVM32_SYSCALL_HALT          0x1000000
 #define UVM32_SYSCALL_YIELD         0x1000001
 #define UVM32_SYSCALL_STACKPROTECT  0x1000002
 
+// Address of External RAM, when offered by host
 #define UVM32_EXTRAM_BASE 0x10000000
 
-#include "uvm32_common_custom.h"
+#endif
+
diff --git a/precompiled/self.bin b/precompiled/self.bin
index d5be60a..69db4b1 100755
Binary files a/precompiled/self.bin and b/precompiled/self.bin differ