diff --git a/vlib/builtin/int_test.v b/vlib/builtin/int_test.v
index 8bafd8fefe..7c162f31a9 100644
--- a/vlib/builtin/int_test.v
+++ b/vlib/builtin/int_test.v
@@ -268,3 +268,12 @@ fn test_int_max() {
 	assert int_max(-5, 5) == 5
 	assert int_max(5, -5) == 5
 }
+
+fn test_big_int() {
+	x := i64(2147483647)
+	if x > -2147483649 && x < 2147483648 {
+		assert true
+	} else {
+		assert false
+	}
+}
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 950599f36e..a69f57cdaa 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -3184,13 +3184,6 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_typ
 			g.write('*')
 		}
 	}
-	if expr is ast.IntegerLiteral {
-		if expected_type in [ast.u64_type, ast.u32_type, ast.u16_type] && expr.val[0] != `-` {
-			g.expr(expr)
-			g.write('U')
-			return
-		}
-	}
 	if (exp_sym.kind == .function && !expected_type.has_option_or_result())
 		|| (g.inside_struct_init && expected_type == ast.voidptr_type
 		&& expected_type != got_type_raw && expr !is ast.StructInit) {
@@ -3814,6 +3807,13 @@ fn (mut g Gen) expr(node_ ast.Expr) {
 				g.write2('-0', node.val[3..])
 			} else {
 				g.write(node.val)
+				val_type := determine_integer_literal_type(node)
+				if val_type in [ast.u32_type, ast.u64_type] {
+					g.write('U')
+				}
+				if val_type in [ast.i64_type, ast.u64_type] {
+					g.write('LL')
+				}
 			}
 		}
 		ast.IsRefType {
@@ -5670,13 +5670,6 @@ fn (mut g Gen) cast_expr(node ast.CastExpr) {
 					}
 				}
 				g.expr(node.expr)
-				if node.expr is ast.IntegerLiteral {
-					if node_typ in [ast.u64_type, ast.u32_type, ast.u16_type] {
-						if !node.expr.val.starts_with('-') {
-							g.write('U')
-						}
-					}
-				}
 				g.write('))')
 			}
 		}
@@ -8519,3 +8512,43 @@ fn (mut g Gen) check_noscan(elem_typ ast.Type) string {
 	}
 	return ''
 }
+
+const hi_32_mask = u64(0xFFFFFFFF00000000)
+const lo_32_mask = u64(0x00000000FFFFFFFF)
+const sign_bit_32 = u32(0x80000000)
+const sign_bit_64 = u64(0x8000000000000000)
+
+fn determine_integer_literal_type(node ast.IntegerLiteral) ast.Type {
+	is_negative := node.val.starts_with('-')
+	if is_negative {
+		uval := node.val.i64()
+		high32 := u32(uval >> 32)
+		low32 := u32(uval)
+		// Check if high 32 bits are all ones (0xFFFFFFFF)
+		// This indicates a 32-bit negative number in two's complement
+		high32_all_ones := high32 == u32(0xFFFFFFFF)
+		// Check if the sign bit (bit 31) is set in low 32 bits
+		// This confirms the number is negative in 32-bit context
+		low32_sign_bit_set := (low32 & sign_bit_32) != 0
+		// If both conditions are true, it's a 32-bit signed integer (i32)
+		// Otherwise, it requires 64-bit representation (i64)
+		return if high32_all_ones && low32_sign_bit_set { ast.i32_type } else { ast.i64_type }
+	} else {
+		uval := node.val.u64()
+		high32_all_zero := (uval & hi_32_mask) == 0
+		if high32_all_zero {
+			low32 := u32(uval)
+			// Check if sign bit (bit 31) is clear (0)
+			// This indicates the number fits in 31 bits (signed 32-bit positive)
+			low32_sign_bit_clear := (low32 & sign_bit_32) == 0
+			// If sign bit is clear, it's a signed 32-bit integer (i32)
+			// Otherwise, it's an unsigned 32-bit integer (u32)
+			return if low32_sign_bit_clear { ast.i32_type } else { ast.u32_type }
+		} else {
+			sign_bit_clear := (uval & sign_bit_64) == 0
+			// If sign bit is clear, it's a signed 64-bit integer (i64)
+			// Otherwise, it's an unsigned 64-bit integer (u64)
+			return if sign_bit_clear { ast.i64_type } else { ast.u64_type }
+		}
+	}
+}
diff --git a/vlib/v/gen/c/testdata/globals_with_weak_tag.c.must_have b/vlib/v/gen/c/testdata/globals_with_weak_tag.c.must_have
index 8dd68e4e51..7b9dcd8f17 100644
--- a/vlib/v/gen/c/testdata/globals_with_weak_tag.c.must_have
+++ b/vlib/v/gen/c/testdata/globals_with_weak_tag.c.must_have
@@ -1,7 +1,7 @@
-u64 VWEAK abc = ((u64)(1U)); // global
-u64 xyz = ((u64)(2U)); // global
-u64 VWEAK weak_1 = ((u64)(4U)); // global
-u64 VWEAK weak_2 = ((u64)(5U)); // global
+u64 VWEAK abc = ((u64)(1)); // global
+u64 xyz = ((u64)(2)); // global
+u64 VWEAK weak_1 = ((u64)(4)); // global
+u64 VWEAK weak_2 = ((u64)(5)); // global
 VV_LOC int main__a_weak_function(void);
 VV_LOC void main__main(void);