diff --git a/src/decrypt.c b/src/decrypt.c
index 1832d6e..3b67ba1 100644
--- a/src/decrypt.c
+++ b/src/decrypt.c
@@ -30,6 +30,7 @@
 #include "decrypt.h"
 #include "ntru_string.h"
 
+#include <stdbool.h>
 #include <string.h>
 
 #include <fmpz_poly.h>
@@ -38,7 +39,7 @@
 
 /*------------------------------------------------------------------------*/
 
-void
+bool
 ntru_decrypt_poly(
 		fmpz_poly_t encr_msg,
 		fmpz_poly_t priv_key,
@@ -48,6 +49,9 @@ ntru_decrypt_poly(
 {
 	fmpz_poly_t a;
 
+	if (!encr_msg || !priv_key || !priv_key_inv || !out_bin || !ctx)
+		return false;
+
 	fmpz_poly_init(a);
 	fmpz_poly_zero(a);
 
@@ -57,6 +61,8 @@ ntru_decrypt_poly(
 	fmpz_poly_mod(out_bin, ctx->p);
 
 	fmpz_poly_clear(a);
+
+	return true;
 }
 
 /*------------------------------------------------------------------------*/
@@ -72,6 +78,9 @@ ntru_decrypt_string(
 	string *decr_msg;
 	fmpz_poly_t **poly_array;
 
+	if (!encr_msg || !encr_msg->len)
+		return NULL;
+
 	poly_array = base64_to_poly_arr(encr_msg, ctx);
 
 	while (*poly_array[i]) {
diff --git a/src/decrypt.h b/src/decrypt.h
index 48b665b..beeb8ff 100644
--- a/src/decrypt.h
+++ b/src/decrypt.h
@@ -32,6 +32,8 @@
 #include "ntru_string.h"
 #include "poly.h"
 
+#include <stdbool.h>
+
 #include <fmpz_poly.h>
 #include <fmpz.h>
 
@@ -47,8 +49,9 @@
  * @param priv_key_inv the inverse polynome to the private key
  * @param out_tern the resulting ternary polynom [out]
  * @param ctx the ntru_context
+ * @return true/false for success/failure
  */
-void
+bool
 ntru_decrypt_poly(
 		fmpz_poly_t encr_msg,
 		fmpz_poly_t priv_key,
@@ -64,6 +67,7 @@ ntru_decrypt_poly(
  * 		the message
  * @param priv_key_inv the inverse polynome to the private key
  * @param ctx the ntru_context
+ * @return the decrypted string or NULL on failure
  */
 string *
 ntru_decrypt_string(