diff --git a/include/polarssl/rsa.h b/include/polarssl/rsa.h
index 7daa05a..a513a77 100644
--- a/include/polarssl/rsa.h
+++ b/include/polarssl/rsa.h
@@ -451,7 +451,7 @@
                       md_type_t md_alg,
                       unsigned int hashlen,
                       const unsigned char *hash,
-                      unsigned char *sig );
+                      const unsigned char *sig );
 
 /**
  * \brief          Perform a PKCS#1 v1.5 verification (RSASSA-PKCS1-v1_5-VERIFY)
@@ -474,7 +474,7 @@
                                  md_type_t md_alg,
                                  unsigned int hashlen,
                                  const unsigned char *hash,
-                                 unsigned char *sig );
+                                 const unsigned char *sig );
 
 /**
  * \brief          Perform a PKCS#1 v2.1 PSS verification (RSASSA-PSS-VERIFY)
@@ -504,7 +504,7 @@
                            md_type_t md_alg,
                            unsigned int hashlen,
                            const unsigned char *hash,
-                           unsigned char *sig );
+                           const unsigned char *sig );
 
 /**
  * \brief          Free the components of an RSA key