diff --git a/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/AdditiveExpressionTest.kt b/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/AdditiveExpressionTest.kt
index fa60523..f102f12 100644
--- a/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/AdditiveExpressionTest.kt
+++ b/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/AdditiveExpressionTest.kt
@@ -11,7 +11,7 @@ class AdditiveExpressionTest {
     @Test fun testUnaryPlus() = runUnaryPlusTests()
     // @Test fun testInverse() = runInverseTests() // TODO
     // @Test fun testGetValue() = runGetValueTests() // TODO
-    @Test fun testIsZero() = runIsZeroTests() // TODO
+    @Test fun testIsZero() = runIsZeroTests()
 
     // @Test fun testToTerm() = runToTermTests()
     // @Test fun testToByte() = runToByteTests() // TODO
diff --git a/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/additive/unaryTests.kt b/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/additive/unaryTests.kt
index b62ed10..775b881 100644
--- a/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/additive/unaryTests.kt
+++ b/exact-numbers/src/test/kotlin/xyz/lbres/exactnumbers/expressions/expression/additive/unaryTests.kt
@@ -5,6 +5,7 @@ import xyz.lbres.exactnumbers.expressions.Expression
 import xyz.lbres.exactnumbers.expressions.expression.* // ktlint-disable no-wildcard-imports no-unused-imports
 import xyz.lbres.exactnumbers.expressions.term.Term
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 
 private val negOne = SimpleExpression(-Term.ONE)
@@ -92,4 +93,16 @@ fun runIsZeroTests() {
     assertTrue(expr.isZero())
 
     // not zero
+    expr = AdditiveExpression(SimpleExpression(Term.fromValues(ExactFraction("-0.0000000000000000001"), emptyList())), Expression.ZERO)
+    assertFalse(expr.isZero())
+
+    partialExpr = MultiplicativeExpression( // 1/2
+        SimpleExpression(Term.fromValues(ExactFraction(2), listOf(pi))),
+        SimpleExpression(Term.fromValues(ExactFraction(1, 4), listOf(piInverse)))
+    )
+    expr = AdditiveExpression(AdditiveExpression(partialExpr, partialExpr), MultiplicativeExpression(partialExpr, partialExpr))
+    assertFalse(expr.isZero())
+
+    expr = AdditiveExpression(AdditiveExpression(simpleExpr1, -simpleExpr3), simpleExpr3)
+    assertFalse(expr.isZero())
 }