diff --git a/pkl-core/src/main/java/org/pkl/core/DataSize.java b/pkl-core/src/main/java/org/pkl/core/DataSize.java
index 5fcb44dbd..76f3a9f76 100644
--- a/pkl-core/src/main/java/org/pkl/core/DataSize.java
+++ b/pkl-core/src/main/java/org/pkl/core/DataSize.java
@@ -247,7 +247,8 @@ public final class DataSize implements Value {
 
   @Override
   public int hashCode() {
-    return Double.hashCode(convertValueTo(DataSizeUnit.BYTES));
+    // adding 0.0 normalizes -0.0 to 0.0, because -0.0 == 0.0 but their hash codes differ
+    return Double.hashCode(convertValueTo(DataSizeUnit.BYTES) + 0.0);
   }
 
   @Override
diff --git a/pkl-core/src/main/java/org/pkl/core/Duration.java b/pkl-core/src/main/java/org/pkl/core/Duration.java
index df38d7eae..2c21d2019 100644
--- a/pkl-core/src/main/java/org/pkl/core/Duration.java
+++ b/pkl-core/src/main/java/org/pkl/core/Duration.java
@@ -222,7 +222,8 @@ public final class Duration implements Value {
 
   @Override
   public int hashCode() {
-    return Double.hashCode(convertValueTo(DurationUnit.NANOS));
+    // adding 0.0 normalizes -0.0 to 0.0, because -0.0 == 0.0 but their hash codes differ
+    return Double.hashCode(convertValueTo(DurationUnit.NANOS) + 0.0);
   }
 
   @Override
diff --git a/pkl-core/src/test/kotlin/org/pkl/core/DataSizeTest.kt b/pkl-core/src/test/kotlin/org/pkl/core/DataSizeTest.kt
index f6fda6fd5..fdf3fff1a 100644
--- a/pkl-core/src/test/kotlin/org/pkl/core/DataSizeTest.kt
+++ b/pkl-core/src/test/kotlin/org/pkl/core/DataSizeTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -121,5 +121,10 @@ class DataSizeTest {
 
     assertThat(size3.hashCode()).isNotEqualTo(size1.hashCode())
     assertThat(size2.hashCode()).isNotEqualTo(size3.hashCode())
+
+    // -0.0 == 0.0, so equal sizes must have equal hash codes
+    assertThat(DataSize(0.0, BYTES)).isEqualTo(DataSize(-0.0, BYTES))
+    assertThat(DataSize(0.0, BYTES).hashCode()).isEqualTo(DataSize(-0.0, BYTES).hashCode())
+    assertThat(DataSize(0.0, BYTES).hashCode()).isEqualTo(DataSize(-0.0, PEBIBYTES).hashCode())
   }
 }
diff --git a/pkl-core/src/test/kotlin/org/pkl/core/DurationTest.kt b/pkl-core/src/test/kotlin/org/pkl/core/DurationTest.kt
index 298d48c6e..690cf6d1c 100644
--- a/pkl-core/src/test/kotlin/org/pkl/core/DurationTest.kt
+++ b/pkl-core/src/test/kotlin/org/pkl/core/DurationTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -285,5 +285,10 @@ class DurationTest {
 
     assertThat(duration3.hashCode()).isNotEqualTo(duration1.hashCode())
     assertThat(duration2.hashCode()).isNotEqualTo(duration3.hashCode())
+
+    // -0.0 == 0.0, so equal durations must have equal hash codes
+    assertThat(Duration(0.0, MILLIS)).isEqualTo(Duration(-0.0, MILLIS))
+    assertThat(Duration(0.0, MILLIS).hashCode()).isEqualTo(Duration(-0.0, MILLIS).hashCode())
+    assertThat(Duration(0.0, NANOS).hashCode()).isEqualTo(Duration(-0.0, DAYS).hashCode())
   }
 }