diff --git a/libcrypto_utils/android_pubkey.c b/libcrypto_utils/android_pubkey.c
index 9cd9aab..3052e52 100644
--- a/libcrypto_utils/android_pubkey.c
+++ b/libcrypto_utils/android_pubkey.c
@@ -20,6 +20,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include <openssl/bn.h>
+
 // Better safe than sorry.
 #if (ANDROID_PUBKEY_MODULUS_SIZE % 4) != 0
 #error RSA modulus size must be multiple of the word size!