diff --git a/src/parser.c b/src/parser.c
index 8eea28ec..fbfb4e1b 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -175,7 +175,10 @@ int read_numeric_constant(char buffer[])
             }
             return value;
         }
-        value = value * 10 + buffer[i++] - '0';
+        if (buffer[0] == '0') /* octal */
+            value = value * 8 + buffer[i++] - '0';
+        else
+            value = value * 10 + buffer[i++] - '0';
     }
     return value;
 }
@@ -612,22 +615,29 @@ void read_numeric_param(block_t *parent, basic_block_t *bb, int is_neg)
         is_neg = 1 - is_neg;
         i++;
     }
-    if ((token[0] == '0') && (token[1] == 'x')) { /* hexadecimal */
-        i = 2;
-        do {
-            c = token[i++];
-            if (is_digit(c))
-                c -= '0';
-            else {
-                c |= 32; /* convert to lower case */
-                if (c >= 'a' && c <= 'f')
-                    c = (c - 'a') + 10;
-                else
-                    error("Invalid numeric constant");
-            }
+    if (token[0] == '0') {
+        if (token[1] == 'x') { /* hexdecimal */
+            i = 2;
+            do {
+                c = token[i++];
+                if (is_digit(c))
+                    c -= '0';
+                else {
+                    c |= 32; /* convert to lower case */
+                    if (c >= 'a' && c <= 'f')
+                        c = (c - 'a') + 10;
+                    else
+                        error("Invalid numeric constant");
+                }
 
-            value = (value * 16) + c;
-        } while (is_hex(token[i]));
+                value = (value * 16) + c;
+            } while (is_hex(token[i]));
+        } else { /* octal */
+            do {
+                c = token[i++] - '0';
+                value = (value * 8) + c;
+            } while (is_digit(token[i]));
+        }
     } else {
         do {
             c = token[i++] - '0';
diff --git a/tests/driver.sh b/tests/driver.sh
index 17ca3352..ce66fd39 100755
--- a/tests/driver.sh
+++ b/tests/driver.sh
@@ -78,6 +78,10 @@ function expr() {
 expr 0 0
 expr 42 42
 
+# octal constant (satisfying re(0[0-7]+))
+expr 10 012
+expr 65 0101
+
 # arithmetic
 expr 42 "24 + 18"
 expr 30 "58 - 28"
@@ -95,6 +99,9 @@ expr 55 "((((((((1 + 2) + 3) + 4) + 5) + 6) + 7) + 8) + 9) + 10"
 expr 55 "1 + (2 + (3 + (4 + (5 + (6 + (7 + (8 + (9 + 10))))))))"
 expr 210 "1 + (2 + (3 + (4 + (5 + (6 + (7 + (8 + (9 + (10 + (11 + (12 + (13 + (14 + (15 + (16 + (17 + (18 + (19 + 20))))))))))))))))))"
 
+expr 11 "1 + 012"   # oct(012) = dec(10)
+expr 25 "017 + 012" # oct(017) = dec(15), oct(012) = dec(10)
+
 # expr 21 "+1+20"
 # expr 10 "-15+(+35-10)"
 
@@ -108,6 +115,16 @@ expr 0 "5 >= 10"
 expr 1 "5 >= 5"
 expr 1 "30 != 20"
 
+# value satisfying re(0[0-7]+) should be parsed as octal
+expr 1 "010 == 8"
+expr 1 "011 < 11"
+expr 0 "021 >= 21"
+expr 1 "(012 - 5) == 5"
+expr 16 "0100 >> 2"
+
+# oct(355) = bin(1110_1101), oct(~355) = bin(0001_0010) = dec(18)
+expr 18 "~0355"
+
 expr 0 "!237"
 expr 18 "~237"
 
@@ -139,12 +156,21 @@ items 10 "int var; var = 10; return var;"
 items 42 "int va; int vb; va = 11; vb = 31; int vc; vc = va + vb; return vc;"
 items 50 "int v; v = 30; v = 50; return v;"
 
+# variable with octal literals
+items 10 "int var; var = 012; return var;"
+items 100 "int var; var = 10 * 012; return var;"
+items 32 "int var; var = 0100 / 2; return var;"
+items 65 "int var; var = 010 << 3; var += 1; return var;"
+
 # if
 items 5 "if (1) return 5; else return 20;"
 items 10 "if (0) return 5; else if (0) return 20; else return 10;"
 items 10 "int a; a = 0; int b; b = 0; if (a) b = 10; else if (0) return a; else if (a) return b; else return 10;"
 items 27 "int a; a = 15; int b; b = 2; if(a - 15) b = 10; else if (b) return a + b + 10; else if (a) return b; else return 10;"
 
+items 8 "if (1) return 010; else return 11;"
+items 10 "int a; a = 012 - 10; int b; b = 0100 - 64; if (a) b = 10; else if (0) return a; else if (a) return b; else return 10;"
+
 # compound
 items 5 "{ return 5; }"
 items 10 "{ int a; a = 5; { a = 5 + a; } return a; }"
@@ -197,6 +223,21 @@ int main() {
 }
 EOF
 
+try_ 55 << EOF
+int fib(int n, int a, int b)
+{
+    if (n == 0)
+        return a;
+    else if (n == 1)
+        return b;
+    return fib(n - 1, b, a + b);
+}
+
+int main() {
+    return fib(012, 0, 1); /* octal(12) = dec(10) */
+}
+EOF
+
 try_ 1 << EOF
 int is_odd(int x);
 
@@ -656,6 +697,15 @@ int main()
 }
 EOF
 
+# octal(155) = dec(109), expect same output with above test suite
+try_output 0 "12 -1" << EOF
+int main()
+{
+    printf("%d %d", -0155 / -9, -0155 % -9);
+    return 0;
+}
+EOF
+
 try_output 0 "1365 0" << EOF
 int main()
 {