diff --git a/include/lib/capnp-c/capnp_c.h b/include/lib/capnp-c/capnp_c.h
index 609826aa0a04c97fcbf3b725916edf8cfe9a6e93..28f171d3e13d02ca3cc3b10462dcf72217900afb 100644
--- a/include/lib/capnp-c/capnp_c.h
+++ b/include/lib/capnp-c/capnp_c.h
@@ -28,6 +28,11 @@ typedef intmax_t ssize_t;
 #include <stddef.h>
 #endif
 
+// AVR does not have ssize_T either
+#ifdef MULTIPASS_ARCH_arduino_nano
+typedef intmax_t ssize_t;
+#endif
+
 // Cross-platform macro ALIGNED_(x) aligns a struct by `x` bytes.
 #ifdef _MSC_VER
 #define ALIGNED_(x) __declspec(align(x))