diff --git a/ion/src/device/shared/usb/Makefile b/ion/src/device/shared/usb/Makefile
index 2e7ae45db..3db2b7d51 100644
--- a/ion/src/device/shared/usb/Makefile
+++ b/ion/src/device/shared/usb/Makefile
@@ -33,6 +33,7 @@ ion_device_usb_src += $(addprefix ion/src/device/shared/usb/stack/descriptor/, \
 
 # DFU code
 
+ion_device_dfu_src += liba/src/abs.c
 ion_device_dfu_src += liba/src/assert.c
 ion_device_dfu_src += liba/src/strlen.c
 ion_device_dfu_src += liba/src/strlcpy.c
diff --git a/liba/Makefile b/liba/Makefile
index 676fa88d0..3639ceb91 100644
--- a/liba/Makefile
+++ b/liba/Makefile
@@ -3,6 +3,7 @@ SFLAGS += -Iliba/include
 liba_src += $(addprefix liba/src/, \
   armv7m/setjmp.s \
   armv7m/longjmp.s \
+  abs.c \
   assert.c \
   bzero.c \
   ctype.c \
diff --git a/liba/include/stdlib.h b/liba/include/stdlib.h
index 6cf0a9654..6c27b3d6e 100644
--- a/liba/include/stdlib.h
+++ b/liba/include/stdlib.h
@@ -13,6 +13,8 @@ void * calloc(size_t count, size_t size);
 
 void abort(void) __attribute__((noreturn));
 
+int abs(int n);
+
 LIBA_END_DECLS
 
 #endif
diff --git a/liba/src/abs.c b/liba/src/abs.c
new file mode 100644
index 000000000..8d0efabdc
--- /dev/null
+++ b/liba/src/abs.c
@@ -0,0 +1,5 @@
+#include <stdlib.h>
+
+int abs(int n) {
+  return n < 0 ? -n : n;
+}
\ No newline at end of file