diff --git a/src/constants/sizes.asm b/src/constants/sizes.asm
index 34a26dd..6aef3e7 100644
--- a/src/constants/sizes.asm
+++ b/src/constants/sizes.asm
@@ -14,10 +14,10 @@ MAX_UINT32		equ	0xFFFFFFFF
 MAX_UINT16		equ	0xFFFF
 MAX_UINT8		equ	0xFF
 
-MIN_INT64		equ	~0x7FFFFFFFFFFFFFFF
-MIN_INT32		equ	~0x7FFFFFFF
-MIN_INT16		equ	~0x7FFF
-MIN_INT8		equ	~0x7F
+MIN_INT64		equ	~MAX_INT64 + 1
+MIN_INT32		equ	~MAX_INT32 + 1
+MIN_INT16		equ	~MAX_INT16 + 1
+MIN_INT8		equ	~MAX_INT8 + 1
 
 MAX_INT64		equ	0x7FFFFFFFFFFFFFFF
 MAX_INT32		equ	0x7FFFFFFF
diff --git a/src/convert.asm b/src/convert.asm
index 1b5b7da..e0d77e3 100644
--- a/src/convert.asm
+++ b/src/convert.asm
@@ -22,16 +22,19 @@ section .text
 ;	r8*	tmp storage rsi (cmov) >> Loop counter for calculating base^n
 ;	r9*	tmp storage rdx (cmov) >> Calculated base^n
 ;	r10*	Stores return value (since RAX is used by IMUL)
+;	r11*	Stores if input is signed (r11b=1) or unsigned (r11b=0) ('-')
 atoi:
 	xor	rax, rax
 	xor	rcx, rcx
 	xor	r10, r10
+	xor	r11b, r11b
 	cmp	byte [rdi], EOS
 	je	.quit
 
 	; -- Test if negative (increase pointer to str, result is always calculated positively. Once reaching '-' again, then NEG)
 	cmp	byte [rdi], '-'
 	jne	.noMinusSign
+	inc	r11b
 	inc	rdi
 	inc	rcx ;make sure .calculateLoop includes minus sign
 
@@ -61,8 +64,8 @@ atoi:
 	mov	rdx, '9'
 	jmp	.getLenLoop
 	.skipBaseNotation:
-	cmp	rcx, 1 ;If '-' was found, using base is invalid
-	je	.quit
+	test	r11b, r11b;If '-' was found, using base is invalid
+	jnz	.quit
 	add	rdi, 2
 
 	; -- Get length of numeric string + test if valid
@@ -149,14 +152,15 @@ atoi:
 
 		.calcNum_cnt:
 		imul	r9
-
-		mov	rdx, -1
-		sub	rdx, r10
-		cmp	rax, rdx
-		;TODO: Add signed checks
-		ja	.overflow
-
+		test	r11b, r11b
+		jz	.checkUnsignedOverflow
 		add	r10, rax
+		jo	.overflow
+		jmp	.continue
+		.checkUnsignedOverflow:
+		add	r10, rax
+		jc	.overflow
+		.continue:
 		dec	rdi
 		inc	r8
 		loop	.calculateLoop
diff --git a/src/tests.asm b/src/tests.asm
index 1326a8c..1f3c49b 100644
--- a/src/tests.asm
+++ b/src/tests.asm
@@ -345,6 +345,10 @@ section .rodata
 	addTest(atoi7, "atoi(''0b00010111'')") ;23
 	addTest(atoi8, "atoi(''0b02010111'')") ;0
 	addTest(atoi9, "atoi(''0xabcdefg'')") ;0
+	addTest(atoi10, "atoi(''18446744073709551615'')") ;MAX_UINT64
+	addTest(atoi11, "atoi(''18446744073709551616'')") ;0
+	addTest(atoi12, "atoi('-9223372036854775807''')") ;MIN_INT64
+	addTest(atoi13, "atoi('-9223372036854775809''')") ;0
 	atoiStr1	db	"079168045",EOS
 	atoiStr2	db	"-079168045",EOS
 	atoiStr3	db	"-0xABCDEF",EOS
@@ -354,6 +358,10 @@ section .rodata
 	atoiStr7	db	"0b00010111",EOS
 	atoiStr8	db	"0b02010111",EOS
 	atoiStr9	db	"0xabcdefg",EOS
+	atoiStr10	db	"18446744073709551615",EOS
+	atoiStr11	db	"18446744073709551616",EOS
+	atoiStr12	db	"-9223372036854775807",EOS
+	atoiStr13	db	"-9223372036854775809",EOS
 	;itoa()
 	addTestHeader(_itoa, "itoa")
 	addTest(itoa1, "// See printf outputs")
@@ -1297,6 +1305,30 @@ _start:
 	lea	rdi, [rel atoiStr9]
 	call	atoi
 	assert_u_eq(0)
+
+	; TEST 10
+	printTest(atoi10)
+	lea	rdi, [rel atoiStr10]
+	call	atoi
+	assert_u_eq(MAX_UINT64)
+
+	; TEST 11
+	printTest(atoi11)
+	lea	rdi, [rel atoiStr11]
+	call	atoi
+	assert_eq(0)
+
+	; TEST 12
+	printTest(atoi12)
+	lea	rdi, [rel atoiStr12]
+	call	atoi
+	assert_eq(MIN_INT64)
+
+	; TEST 13
+	printTest(atoi13)
+	lea	rdi, [rel atoiStr13]
+	call	atoi
+	assert_eq(0)
 %endif
 
 ;--- itoa()