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 76f3a9f76..8c46de553 100644
--- a/pkl-core/src/main/java/org/pkl/core/DataSize.java
+++ b/pkl-core/src/main/java/org/pkl/core/DataSize.java
@@ -253,6 +253,8 @@ public final class DataSize implements Value {
 
   @Override
   public String toString() {
-    return MathUtils.isMathematicalInteger(value) ? (long) value + "." + unit : value + "." + unit;
+    return MathUtils.isMathematicalIntegerFittingLong(value)
+        ? (long) value + "." + unit
+        : value + "." + unit;
   }
 }
diff --git a/pkl-core/src/main/java/org/pkl/core/runtime/VmDataSize.java b/pkl-core/src/main/java/org/pkl/core/runtime/VmDataSize.java
index e23760d31..3d1c89f25 100644
--- a/pkl-core/src/main/java/org/pkl/core/runtime/VmDataSize.java
+++ b/pkl-core/src/main/java/org/pkl/core/runtime/VmDataSize.java
@@ -157,7 +157,9 @@ public final class VmDataSize extends VmValue implements Comparable<VmDataSize>
 
   @Override
   public String toPklString() {
-    return MathUtils.isMathematicalInteger(value) ? (long) value + "." + unit : value + "." + unit;
+    return MathUtils.isMathematicalIntegerFittingLong(value)
+        ? (long) value + "." + unit
+        : value + "." + unit;
   }
 
   private double convertValueTo(DataSizeUnit other) {
diff --git a/pkl-core/src/main/java/org/pkl/core/stdlib/base/DataSizeNodes.java b/pkl-core/src/main/java/org/pkl/core/stdlib/base/DataSizeNodes.java
index 660874462..454ad5fb8 100644
--- a/pkl-core/src/main/java/org/pkl/core/stdlib/base/DataSizeNodes.java
+++ b/pkl-core/src/main/java/org/pkl/core/stdlib/base/DataSizeNodes.java
@@ -29,12 +29,12 @@ public final class DataSizeNodes {
   @ImportStatic(MathUtils.class)
   @PklName("value")
   public abstract static class valueProperty extends ExternalPropertyNode {
-    @Specialization(guards = "isMathematicalInteger(self.getValue())")
+    @Specialization(guards = "isMathematicalIntegerFittingLong(self.getValue())")
     protected long evalInt(VmDataSize self) {
       return (long) self.getValue();
     }
 
-    @Specialization(guards = "!isMathematicalInteger(self.getValue())")
+    @Specialization(guards = "!isMathematicalIntegerFittingLong(self.getValue())")
     protected double evalFloat(VmDataSize self) {
       return self.getValue();
     }
diff --git a/pkl-core/src/main/java/org/pkl/core/stdlib/base/DurationNodes.java b/pkl-core/src/main/java/org/pkl/core/stdlib/base/DurationNodes.java
index 60ddd7a31..060afec5f 100644
--- a/pkl-core/src/main/java/org/pkl/core/stdlib/base/DurationNodes.java
+++ b/pkl-core/src/main/java/org/pkl/core/stdlib/base/DurationNodes.java
@@ -31,12 +31,12 @@ public final class DurationNodes {
   @ImportStatic(MathUtils.class)
   @PklName("value")
   public abstract static class valueProperty extends ExternalPropertyNode {
-    @Specialization(guards = "isMathematicalInteger(self.getValue())")
+    @Specialization(guards = "isMathematicalIntegerFittingLong(self.getValue())")
     protected long evalInt(VmDuration self) {
       return (long) self.getValue();
     }
 
-    @Specialization(guards = "!isMathematicalInteger(self.getValue())")
+    @Specialization(guards = "!isMathematicalIntegerFittingLong(self.getValue())")
     protected double evalFloat(VmDuration self) {
       return self.getValue();
     }
diff --git a/pkl-core/src/main/java/org/pkl/core/util/DurationUtils.java b/pkl-core/src/main/java/org/pkl/core/util/DurationUtils.java
index 88b86739e..8b13dc998 100644
--- a/pkl-core/src/main/java/org/pkl/core/util/DurationUtils.java
+++ b/pkl-core/src/main/java/org/pkl/core/util/DurationUtils.java
@@ -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.
@@ -21,7 +21,9 @@ public final class DurationUtils {
   private DurationUtils() {}
 
   public static String toPklString(double value, DurationUnit unit) {
-    return MathUtils.isMathematicalInteger(value) ? (long) value + "." + unit : value + "." + unit;
+    return MathUtils.isMathematicalIntegerFittingLong(value)
+        ? (long) value + "." + unit
+        : value + "." + unit;
   }
 
   // see: https://standards.calconnect.org/csd/cc-18011.html#toc32
diff --git a/pkl-core/src/main/java/org/pkl/core/util/MathUtils.java b/pkl-core/src/main/java/org/pkl/core/util/MathUtils.java
index c060f0207..6f598c2a3 100644
--- a/pkl-core/src/main/java/org/pkl/core/util/MathUtils.java
+++ b/pkl-core/src/main/java/org/pkl/core/util/MathUtils.java
@@ -55,6 +55,15 @@ public final class MathUtils {
                 <= StrictMath.getExponent(x));
   }
 
+  /**
+   * Returns {@code true} if {@code x} is a mathematical integer that can be represented exactly as
+   * a {@code long}.
+   */
+  @TruffleBoundary
+  public static boolean isMathematicalIntegerFittingLong(double x) {
+    return isMathematicalInteger(x) && MIN_LONG_AS_DOUBLE <= x && x < MAX_LONG_AS_DOUBLE_PLUS_ONE;
+  }
+
   /**
    * Returns {@code true} if {@code x} represents a power of two.
    *
diff --git a/pkl-core/src/test/files/LanguageSnippetTests/input/api/durationValueSaturation.pkl b/pkl-core/src/test/files/LanguageSnippetTests/input/api/durationValueSaturation.pkl
new file mode 100644
index 000000000..171bd923c
--- /dev/null
+++ b/pkl-core/src/test/files/LanguageSnippetTests/input/api/durationValueSaturation.pkl
@@ -0,0 +1,19 @@
+amends "../snippetTest.pkl"
+
+facts {
+  ["value"] {
+    1e300.d.value == 1e300
+    1e300.b.value == 1e300
+    1.0E18.d.value == 1000000000000000000
+    7.d.value == 7
+    2.2.h.value == 2.2
+  }
+}
+
+examples {
+  ["display"] {
+    1e300.d
+    1e300.b
+    7.d
+  }
+}
diff --git a/pkl-core/src/test/files/LanguageSnippetTests/output/api/durationValueSaturation.pcf b/pkl-core/src/test/files/LanguageSnippetTests/output/api/durationValueSaturation.pcf
new file mode 100644
index 000000000..684d52083
--- /dev/null
+++ b/pkl-core/src/test/files/LanguageSnippetTests/output/api/durationValueSaturation.pcf
@@ -0,0 +1,16 @@
+facts {
+  ["value"] {
+    true
+    true
+    true
+    true
+    true
+  }
+}
+examples {
+  ["display"] {
+    1.0E300.d
+    1.0E300.b
+    7.d
+  }
+}
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 fdf3fff1a..93e971f53 100644
--- a/pkl-core/src/test/kotlin/org/pkl/core/DataSizeTest.kt
+++ b/pkl-core/src/test/kotlin/org/pkl/core/DataSizeTest.kt
@@ -127,4 +127,18 @@ class DataSizeTest {
     assertThat(DataSize(0.0, BYTES).hashCode()).isEqualTo(DataSize(-0.0, BYTES).hashCode())
     assertThat(DataSize(0.0, BYTES).hashCode()).isEqualTo(DataSize(-0.0, PEBIBYTES).hashCode())
   }
+
+  @Test
+  fun `toString()`() {
+    assertThat(DataSize(3.0, BYTES).toString()).isEqualTo("3.b")
+    assertThat(DataSize(1.5, BYTES).toString()).isEqualTo("1.5.b")
+    assertThat(DataSize(1e18, BYTES).toString()).isEqualTo("1000000000000000000.b")
+    // -2^63 still fits into a `long`
+    assertThat(DataSize(-9.223372036854776E18, BYTES).toString())
+      .isEqualTo("-9223372036854775808.b")
+    // values too large to fit into a `long` are printed in their `double` form,
+    // instead of saturating to 9223372036854775807
+    assertThat(DataSize(9.223372036854776E18, BYTES).toString()).isEqualTo("9.223372036854776E18.b")
+    assertThat(DataSize(1e300, PETABYTES).toString()).isEqualTo("1.0E300.pb")
+  }
 }
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 690cf6d1c..955954fa2 100644
--- a/pkl-core/src/test/kotlin/org/pkl/core/DurationTest.kt
+++ b/pkl-core/src/test/kotlin/org/pkl/core/DurationTest.kt
@@ -291,4 +291,18 @@ class DurationTest {
     assertThat(Duration(0.0, MILLIS).hashCode()).isEqualTo(Duration(-0.0, MILLIS).hashCode())
     assertThat(Duration(0.0, NANOS).hashCode()).isEqualTo(Duration(-0.0, DAYS).hashCode())
   }
+
+  @Test
+  fun `toString()`() {
+    assertThat(Duration(3.0, DAYS).toString()).isEqualTo("3.d")
+    assertThat(Duration(1.5, DAYS).toString()).isEqualTo("1.5.d")
+    assertThat(Duration(1e18, DAYS).toString()).isEqualTo("1000000000000000000.d")
+    // -2^63 still fits into a `long`
+    assertThat(Duration(-9.223372036854776E18, DAYS).toString()).isEqualTo("-9223372036854775808.d")
+    // values too large to fit into a `long` are printed in their `double` form,
+    // instead of saturating to 9223372036854775807
+    assertThat(Duration(9.223372036854776E18, DAYS).toString()).isEqualTo("9.223372036854776E18.d")
+    assertThat(Duration(1e300, DAYS).toString()).isEqualTo("1.0E300.d")
+    assertThat(Duration(-1e300, DAYS).toString()).isEqualTo("-1.0E300.d")
+  }
 }