diff --git a/strint.asm b/strint.asm
index 2f258e0..84bebbc 100644
--- a/strint.asm
+++ b/strint.asm
@@ -2,7 +2,7 @@
 ; r1 - Partially parsed output integer
 ; r2 - Parsing position
 ; r3 - Character being parsed
-; r4 - Flag set if negative
+; r4 - Set to -1 if the input is negative
 
 ; Convert string to integer
 ; Arguments:
@@ -44,8 +44,9 @@ je atoi_hex_loop
 
 ; FALLTHROUGH: not a valid prefix, but we did see a zero
 atoi_done:
-add r1, r1, r4
+add r1, r1, r4          ; If r4 is -1, negate r1. Else it's 0 and no effect.
 xor r1, r1, r4
+mov flags, 0            ; No error
 jmp r13
 
 ; Convert decimal string to integer
@@ -60,8 +61,15 @@ jmp r13
 pub atoi_dec:
 mov r2, r1
 mov r1, 0
+mov r4, 0
+load_8 r3, [r2]
+cmp r3, 0x2D ; '-'
+jne atoi_dec_positive
+sub r4, zr, 1           ; Set r4 to -1
+add r2, r2, 1
 atoi_dec_loop:
 load_8 r3, [r2]
+atoi_dec_positive:
 cmp r3, 0x30 ; '0'
 jl atoi_done
 cmp r3, 0x39 ; '9'
@@ -86,6 +94,13 @@ jmp atoi_dec_loop
 pub atoi_bin:
 mov r2, r1
 mov r1, 0
+mov r4, 0
+load_8 r3, [r2]
+cmp r3, 0x2D ; '-'
+jne atoi_bin_positive
+sub r4, zr, 1           ; Set r4 to -1
+add r2, r2, 1
+atoi_bin_positive:
 load_16 r3, [r2]        ; check for prefix
 and r3, r3, 0xFF5F      ; to uppercase
 cmp r3, 0x3042 ; "0B"
@@ -115,6 +130,13 @@ jmp atoi_bin_loop
 pub atoi_oct:
 mov r2, r1
 mov r1, 0
+mov r4, 0
+load_8 r3, [r2]
+cmp r3, 0x2D ; '-'
+jne atoi_oct_positive
+sub r4, zr, 1           ; Set r4 to -1
+add r2, r2, 1
+atoi_oct_positive:
 load_16 r3, [r2]        ; check for prefix
 and r3, r3, 0xFF5F      ; to uppercase
 cmp r3, 0x304F ; "0O"
@@ -144,6 +166,13 @@ jmp atoi_oct_loop
 pub atoi_hex:
 mov r2, r1
 mov r1, 0
+mov r4, 0
+load_8 r3, [r2]
+cmp r3, 0x2D ; '-'
+jne atoi_hex_positive
+sub r4, zr, 1           ; Set r4 to -1
+add r2, r2, 1
+atoi_hex_positive:
 load_16 r3, [r2]        ; check for prefix
 and r3, r3, 0xFF5F      ; to uppercase
 cmp r3, 0x3058 ; "0X"