diff --git a/src/fast_forward.cc b/src/fast_forward.cc
index 30531c60ee2..4bc371055eb 100644
--- a/src/fast_forward.cc
+++ b/src/fast_forward.cc
@@ -404,6 +404,7 @@ static int fallible_read_byte(Task* t, remote_ptr<uint8_t> ip) {
   return byte;
 }
 
+#if defined(__i386__) || defined(__x86_64__)
 bool is_x86_string_instruction_at(Task* t, remote_code_ptr ip) {
   bool found_rep = false;
   remote_ptr<uint8_t> bare_ip = ip.to_data_ptr<uint8_t>();
@@ -421,6 +422,7 @@ bool is_x86_string_instruction_at(Task* t, remote_code_ptr ip) {
     ++bare_ip;
   }
 }
+#endif
 
 static bool is_string_instruction_before(Task* t, remote_code_ptr ip) {
   remote_ptr<uint8_t> bare_ip = ip.to_data_ptr<uint8_t>();