diff --git a/src/runtime/SYSTEM.c b/src/runtime/SYSTEM.c
index a1b2cb14..39c09fe7 100644
--- a/src/runtime/SYSTEM.c
+++ b/src/runtime/SYSTEM.c
@@ -37,13 +37,13 @@ INT64 SYSTEM_DIV(INT64 x, INT64 y)
 
 INT64 SYSTEM_MOD(INT64 x, INT64 y)
 {
-  if (x == 0) return 0;
-  if (x >= 0)
-    if (y >= 0) {return x % y;}
-    else        {return (y+1) + ((x-1) % (-y));}
-  else
-    if (y >= 0) {return (y-1) - ((-x-1) % y);}
-    else        {return -((-x) % (-y));}
+  if (x == 0) {return 0;}
+  INT64 m = x % y;
+  if (m < 0)
+  {
+    m = (y < 0) ? m - y : m + y;
+  }
+  return m;
 }
 
 INT64 SYSTEM_ENTIER(double x)
diff --git a/src/test/confidence/language/TestLanguage.mod b/src/test/confidence/language/TestLanguage.mod
index 7399b006..be09a50a 100644
--- a/src/test/confidence/language/TestLanguage.mod
+++ b/src/test/confidence/language/TestLanguage.mod
@@ -4,6 +4,8 @@ IMPORT SYSTEM, Console;
 
   VAR gz: LONGREAL;
 
+PROCEDURE -cpumod(x, y: INTEGER): INTEGER "(INT64)(x % y)";
+
 PROCEDURE TestShiftResult(of, by, actual, expected: LONGINT; msg: ARRAY OF CHAR);
 BEGIN
   IF actual # expected THEN
@@ -172,7 +174,7 @@ END TestValue;
 PROCEDURE side(i: INTEGER): INTEGER; BEGIN RETURN i END side;
 
 PROCEDURE DivMod;
-  VAR i,j: INTEGER;
+  VAR i,j, m: INTEGER;
 BEGIN
   j := 2;
   i :=  4;  TestValue(i DIV j, 2, "4 DIV 2");       TestValue(side(i) DIV side(j),  2, "side(4) DIV side(2)");
@@ -203,20 +205,44 @@ BEGIN
   i :=  6; j :=  3; TestValue(i MOD j, i - ((i DIV j) * j), "6 MOD 3");
   i :=  7; j :=  3; TestValue(i MOD j, i - ((i DIV j) * j), "7 MOD 3");
 
-  i := -4; j :=  3; TestValue(i MOD j, i - ((i DIV j) * j), "-4 MOD 3");
-  i := -5; j :=  3; TestValue(i MOD j, i - ((i DIV j) * j), "-5 MOD 3");
-  i := -6; j :=  3; TestValue(i MOD j, i - ((i DIV j) * j), "-6 MOD 3");
-  i := -7; j :=  3; TestValue(i MOD j, i - ((i DIV j) * j), "-7 MOD 3");
+  i := -4; j :=  3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-4 MOD 3");
+  i := -5; j :=  3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-5 MOD 3");
+  i := -6; j :=  3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-6 MOD 3");
+  i := -7; j :=  3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-7 MOD 3");
 
-  i :=  4; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "4 MOD -3");
-  i :=  5; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "5 MOD -3");
-  i :=  6; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "6 MOD -3");
-  i :=  7; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "7 MOD -3");
+  i :=  4; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "4 MOD -3");
+  i :=  5; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "5 MOD -3");
+  i :=  6; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "6 MOD -3");
+  i :=  7; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "7 MOD -3");
 
-  i := -4; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "-4 MOD -3");
-  i := -5; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "-5 MOD -3");
-  i := -6; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "-6 MOD -3");
-  i := -7; j := -3; TestValue(i MOD j, i - ((i DIV j) * j), "-7 MOD -3");
+  i := -4; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-4 MOD -3");
+  i := -5; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-5 MOD -3");
+  i := -6; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-6 MOD -3");
+  i := -7; j := -3;
+  m := cpumod(i, j); IF m < 0 THEN IF j < 0 THEN m := m - j ELSE m := m + j END END;
+  TestValue(i MOD j, m, "-7 MOD -3");
 END DivMod;