diff --git a/src/lib.rs b/src/lib.rs
index 0b341c8..229c562 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+#![no_std]
+
 const SHA1_CONST: &[u32] = &[0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0];
 
 pub struct SHA1Hash {