diff --git a/src/main/java/org/apache/commons/lang3/time/Instants.java b/src/main/java/org/apache/commons/lang3/time/Instants.java
index 8532afaf9fa..094cb431982 100644
--- a/src/main/java/org/apache/commons/lang3/time/Instants.java
+++ b/src/main/java/org/apache/commons/lang3/time/Instants.java
@@ -17,6 +17,7 @@
 
 package org.apache.commons.lang3.time;
 
+import java.time.Duration;
 import java.time.Instant;
 
 /**
@@ -86,11 +87,13 @@ public static Instant toInstant(final Instant instant, final Instant defaultInst
      * @return long The duration in milliseconds since the given Instant.
      */
     public static long toMillisSince(final Instant instant) {
-        final Instant instant2 = toInstant(instant);
+        // The sign of the duration is the opposite of the sign of the instant's epoch second: an instant far in the past
+        // yields a large positive duration, an instant far in the future a large negative one. Bind on the duration.
+        final Duration duration = DurationUtils.since(toInstant(instant));
         try {
-            return DurationUtils.since(instant2).toMillis();
+            return duration.toMillis();
         } catch (final ArithmeticException e) {
-            return toBound(instant2, Long.MIN_VALUE, Long.MAX_VALUE);
+            return duration.isNegative() ? Long.MIN_VALUE : Long.MAX_VALUE;
         }
     }
 
diff --git a/src/test/java/org/apache/commons/lang3/time/InstantsTest.java b/src/test/java/org/apache/commons/lang3/time/InstantsTest.java
index 0a7bfdb9f47..1da2587478d 100644
--- a/src/test/java/org/apache/commons/lang3/time/InstantsTest.java
+++ b/src/test/java/org/apache/commons/lang3/time/InstantsTest.java
@@ -179,23 +179,21 @@ void testToMillisSinceFutureInstantIsNegative() {
     }
 
     /**
-     * {@link Instant#MAX} (positive epoch second): the huge negative duration from Instant.MAX to now
-     * overflows {@code long} millis; the bound is {@link Long#MAX_VALUE} because the instant's epoch
-     * second is positive.
+     * {@link Instant#MAX} is in the future, so the duration from it to now is negative and underflows {@code long}
+     * millis; the bound is {@link Long#MIN_VALUE}.
      */
     @Test
-    void testToMillisSinceInstantMaxOverflowReturnsMaxValue() {
-        assertEquals(Long.MAX_VALUE, Instants.toMillisSince(Instant.MAX));
+    void testToMillisSinceInstantMaxUnderflowReturnsMinValue() {
+        assertEquals(Long.MIN_VALUE, Instants.toMillisSince(Instant.MAX));
     }
 
     /**
-     * {@link Instant#MIN} (negative epoch second): the huge positive duration from Instant.MIN to now
-     * overflows {@code long} millis; the bound is {@link Long#MIN_VALUE} because the instant's epoch
-     * second is negative.
+     * {@link Instant#MIN} is in the past, so the duration from it to now is positive and overflows {@code long}
+     * millis; the bound is {@link Long#MAX_VALUE}.
      */
     @Test
-    void testToMillisSinceInstantMinOverflowReturnsMinValue() {
-        assertEquals(Long.MIN_VALUE, Instants.toMillisSince(Instant.MIN));
+    void testToMillisSinceInstantMinOverflowReturnsMaxValue() {
+        assertEquals(Long.MAX_VALUE, Instants.toMillisSince(Instant.MIN));
     }
 
     /**