diff --git a/src/int_to_string.asm b/src/int_to_string.asm
index 3b30768..b67f271 100644
--- a/src/int_to_string.asm
+++ b/src/int_to_string.asm
@@ -13,20 +13,33 @@ include errno
 pub auto:
 cmp r4, 2
 je bin
+cmp r4, 8
+je oct
 mov flags, errno.INTTOSTR_BAD_BASE
 jmp r13
 
+; The output buffer is too small for this integer
+badbuffer:
+mov flags, errno.INTTOSTR_BAD_BUFFER
+jmp r13
+
+; All digits have been output. Null terminate and exit.
+done:
+store_8 [r2], zr
+mov flags, errno.OK
+jmp r13
+
 ; Convert integer to binary string
 ; Arguments:
 ; r1 - Integer
-; r2 - Start of buffer (assumed 'big enough')
-; r3 - Buffer length (ignored)
+; r2 - Start of buffer
+; r3 - Buffer length
 ; Result:
 ; none
 ; Clobbers:
 ; flags
 ; r4 - counter
-; r5 - result character
+; r5 - character
 pub bin:
 mov r4, 31
 cmp r2, 2
@@ -57,10 +70,43 @@ and r5, r5, 1
 sub r4, r4, 1
 jmp bin_print
 
-badbuffer:
-mov flags, errno.INTTOSTR_BAD_BUFFER
-jmp r13
+; Convert integer to octal string
+; Arguments:
+; r1 - Integer
+; r2 - Start of buffer
+; r3 - Buffer length
+; Result:
+; none
+; Clobbers:
+; flags
+; r4 - input counter
+; r5 - character
+; r6 - output size counter
+pub oct:
+mov r4, 30
+mov r6, 12
 
-done:
-store_8 [r2], zr
-jmp r13
+oct_find_one:
+lsr r5, r1, r4          ; Select bit and advance counter
+and r5, r5, 7
+sub r4, r4, 3
+sub r6, r6, 1
+
+cmp r4, 0               ; Start printing if last bit ...
+jl oct_print
+cmp r5, zr              ; .. or if nonzero
+je oct_find_one
+
+cmp r6, r3              ; Check buffer size
+ja badbuffer
+
+oct_print:
+add r5, r5, 0x30 ; '0'  ; Add digit to buffer
+store_8 [r2], r5
+add r2, r2, 1
+cmp r4, 0               ; Done if last bit
+jl done
+lsr r5, r1, r4          ; Select bit and advance counter
+and r5, r5, 7
+sub r4, r4, 3
+jmp oct_print
diff --git a/tests/int_to_string_test.asm b/tests/int_to_string_test.asm
index 2da2da9..51a1424 100644
--- a/tests/int_to_string_test.asm
+++ b/tests/int_to_string_test.asm
@@ -34,6 +34,7 @@ jl next_test
 ; Done
 halt
 
+
 include ../src/stdlib
 
 @0x20000
@@ -43,7 +44,9 @@ tests:
 @0x20000 U32 0b0        U8 2  "0\0"
 @0x20040 U32 0xFFFFFFFF U8 2  "11111111111111111111111111111111\0"
 @0x20080 U32 0b101010   U8 2  "101010\0"
-@0x200c0
+@0x200c0 U32 0o640      U8 8  "640\0"
+@0x20100 U32 0xFFFFFFFF U8 8  "37777777777\0"
+@0x20140
 end_of_tests:
 scratch: U1024 0