diff --git a/src/int_to_string.asm b/src/int_to_string.asm
index ceb166f..567c609 100644
--- a/src/int_to_string.asm
+++ b/src/int_to_string.asm
@@ -17,6 +17,8 @@ cmp r4, 8
 je oct
 cmp r4, 16
 je hex
+cmp r4, 10
+jmp dec
 mov flags, errno.INTTOSTR_BAD_BASE
 jmp r13
 
@@ -52,7 +54,7 @@ lsr r5, r1, r4          ; Select bit and advance counter
 and r5, r5, 1
 sub r4, r4, 1
 
-cmp r4, 0               ; Start printing if last bit ...
+cmp r4, zr              ; Start printing if last bit ...
 jl bin_print
 cmp r5, zr              ; .. or if nonzero
 je bin_find_one
@@ -65,7 +67,7 @@ bin_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
+cmp r4, zr              ; Done if last bit
 jl done
 lsr r5, r1, r4          ; Select bit and advance counter
 and r5, r5, 1
@@ -94,7 +96,7 @@ and r5, r5, 7
 sub r4, r4, 3
 sub r6, r6, 1
 
-cmp r4, 0               ; Start printing if last bit ...
+cmp r4, zr              ; Start printing if last bit ...
 jl oct_print
 cmp r5, zr              ; .. or if nonzero
 je oct_find_one
@@ -106,7 +108,7 @@ 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
+cmp r4, zr              ; Done if last bit
 jl done
 lsr r5, r1, r4          ; Select bit and advance counter
 and r5, r5, 7
@@ -132,7 +134,7 @@ lsr r5, r1, r4          ; Select bit and advance counter
 and r5, r5, 0xF
 sub r4, r4, 4
 
-cmp r4, 0               ; Start printing if last bit ...
+cmp r4, zr              ; Start printing if last bit ...
 jl hex_print
 cmp r5, zr              ; .. or if nonzero
 je hex_find_one
@@ -150,9 +152,88 @@ add r5, r5, 0x07 ; 'A' - '0' - 10
 hex_no_letter:
 store_8 [r2], r5
 add r2, r2, 1
-cmp r4, 0               ; Done if last bit
+cmp r4, zr              ; Done if last bit
 jl done
 lsr r5, r1, r4          ; Select bit and advance counter
 and r5, r5, 0xF
 sub r4, r4, 4
 jmp hex_print
+
+; Convert integer to decimal string
+; Arguments:
+; r1 - Integer
+; r2 - Start of buffer
+; r3 - Buffer length
+; Result:
+; none
+; Clobbers:
+; flags
+; r4, r5
+pub dec:
+mov r4, 0x5F5
+lsl r4, r4, 16
+add r4, r4, 0xE100 ; 100 million; 8 digits
+cmp r1, r4
+jl dec_small
+; TODO large
+
+
+; Small numbers have at least most 8 digits, thus their BCD form fits in
+; one register. Bit 26 is the highest which can be set.
+;
+; Utilizes double dabble
+; r4, r5 are loop counters
+;
+; for( r4 = 24 ; r4 >= 0 ; r4-- )
+;   for( r5 = r4 ; r5 <= 28 ; r5+= 4 )
+;     if( ((r1 >> r5) & 0xF) >= 5 )
+;       r1 += 3 << r5
+dec_small:
+mov r4, 24
+dec_small_dabble_outer:
+mov r5, r4
+dec_small_dabble_inner:
+lsr flags, r1, r5
+and flags, flags, 0xF
+cmp flags, 5
+jl dec_small_dabble_noinc
+mov flags, 3
+lsl flags, flags, r5
+add r1, r1, flags
+dec_small_dabble_noinc:
+add r5, r5, 4
+cmp r5, 28
+jl dec_small_dabble_inner
+sub r4, r4, 1
+cmp r4, zr
+jg dec_small_dabble_outer
+
+; Print the BCD in r1
+; r4 is a counter
+; r5 is the output character
+mov r4, 28
+dec_find_one:
+lsr r5, r1, r4          ; Select bit and advance counter
+and r5, r5, 0xF
+sub r4, r4, 4
+
+cmp r4, zr               ; Start printing if last bit ...
+jl dec_print
+cmp r5, zr              ; .. or if nonzero
+je dec_find_one
+
+lsr flags, r5, 2        ; Check buffer size
+add flags, flags, 3
+cmp flags, r3
+ja badbuffer
+
+dec_print:
+add r5, r5, 0x30 ; '0'  ; Add digit to buffer
+store_8 [r2], r5
+add r2, r2, 1
+cmp r4, zr              ; Done if last bit
+jl done
+lsr r5, r1, r4          ; Select bit and advance counter
+and r5, r5, 0xF
+sub r4, r4, 4
+jmp dec_print
diff --git a/tests/int_to_string_test.asm b/tests/int_to_string_test.asm
index e9b76cd..ecac19b 100644
--- a/tests/int_to_string_test.asm
+++ b/tests/int_to_string_test.asm
@@ -52,7 +52,10 @@ tests:
 @0x201c0 U32 0x32fF6    U8 16 "32FF6\0"
 @0x20200 U32 0xdeadbeef U8 16 "DEADBEEF\0"
 @0x20240 U32 0xFFFFFFFF U8 16 "FFFFFFFF\0"
-@0x20280
+@0x20280 U32 0          U8 10 "0\0"
+@0x202c0 U32 42069      U8 10 "42069\0"
+@0x20300 U32 12345678   U8 10 "12345678\0"
+@0x20340
 end_of_tests:
 scratch: U1024 0