diff --git a/quantecon/_inequality.py b/quantecon/_inequality.py
index 293f1555..952787e6 100644
--- a/quantecon/_inequality.py
+++ b/quantecon/_inequality.py
@@ -4,7 +4,7 @@
 """
 
 import numpy as np
-from numba import njit, prange
+from numba import njit
 
 
 @njit
@@ -54,7 +54,7 @@ def lorenz_curve(y):
     return cum_people, cum_income
 
 
-@njit(parallel=True)
+@njit
 def gini_coefficient(y):
     r"""
     Implements the Gini inequality index
@@ -76,11 +76,13 @@ def gini_coefficient(y):
     https://en.wikipedia.org/wiki/Gini_coefficient
     """
     n = len(y)
-    i_sum = np.zeros(n)
-    for i in prange(n):
-        for j in range(n):
-            i_sum[i] += abs(y[i] - y[j])
-    return np.sum(i_sum) / (2 * n * np.sum(y))
+    y_s = np.sort(y)
+    i_weighted = 0.0
+    total = 0.0
+    for i in range(n):
+        i_weighted += (i + 1) * y_s[i]
+        total += y_s[i]
+    return (2 * i_weighted) / (n * total) - (n + 1) / n
 
 
 def shorrocks_index(A):
@@ -152,4 +154,3 @@ def rank_size(data, c=1.0):
     rank_data = np.arange(len(w)) + 1
     size_data = w
     return rank_data, size_data
-
diff --git a/quantecon/tests/test_inequality.py b/quantecon/tests/test_inequality.py
index be682396..0aa968cb 100644
--- a/quantecon/tests/test_inequality.py
+++ b/quantecon/tests/test_inequality.py
@@ -59,6 +59,11 @@ def test_gini_coeff():
     coeff = gini_coefficient(y)
     assert_allclose(expected, coeff, rtol=1e-01)
 
+    # Regression against the pairwise definition
+    y = np.array([1.0, 2.0, 4.0, 8.0])
+    expected = np.abs(y[:, None] - y).sum() / (2 * len(y) * y.sum())
+    assert_allclose(expected, gini_coefficient(y))
+
     # Tests Weibull: G = 1 - 2**(-1/a)
     a = np.random.randint(2, 15)
     expected = 1 - 2 ** (-1 / a)
@@ -130,4 +135,3 @@ def test_rank_size():
     r_sqval_exp = r_value_exp**2
 
     assert_raises(AssertionError, assert_allclose, r_sqval_exp, 1, rtol=1e-3)
-