diff --git a/src/java.base/share/classes/java/util/Locale.java b/src/java.base/share/classes/java/util/Locale.java
index f600afbb007a6..abd60dab71058 100644
--- a/src/java.base/share/classes/java/util/Locale.java
+++ b/src/java.base/share/classes/java/util/Locale.java
@@ -3204,18 +3204,20 @@ public LanguageRange(String range) {
          *
          * @param range  a language range
          * @param weight a weight value between {@code MIN_WEIGHT} and
-         *     {@code MAX_WEIGHT}
+         *     {@code MAX_WEIGHT}, inclusive
          * @throws NullPointerException if the given {@code range} is
          *     {@code null}
          * @throws IllegalArgumentException if the given {@code range} does not
-         * comply with the syntax of the language range mentioned in RFC 4647
-         * or if the given {@code weight} is less than {@code MIN_WEIGHT}
-         * or greater than {@code MAX_WEIGHT}
+         * comply with the syntax of the language range mentioned in RFC 4647,
+         * or if the given {@code weight} is {@code Double.NaN}, less than {@code
+         * MIN_WEIGHT} or greater than {@code MAX_WEIGHT}
          */
         public LanguageRange(String range, double weight) {
             Objects.requireNonNull(range);
-            if (weight < MIN_WEIGHT || weight > MAX_WEIGHT) {
-                throw new IllegalArgumentException("weight=" + weight);
+            if (weight < MIN_WEIGHT || weight > MAX_WEIGHT || Double.isNaN(weight)) {
+                throw new IllegalArgumentException(
+                        "The weight " + weight + " must be between "
+                        + MIN_WEIGHT + " and " + MAX_WEIGHT + ", inclusive.");
             }
 
             range = range.toLowerCase(Locale.ROOT);
@@ -3338,6 +3340,11 @@ public double getWeight() {
          * matching locale (or language tag) even if the application or system
          * offers only {@code "he"} as a supported locale (or language tag).
          *
+         * @implNote This implementation interprets weights within the {@code ranges}
+         * string using {@link Double#parseDouble(String)}. As a result, some
+         * non-RFC 2616 forms of otherwise in-range values, such as leading
+         * signs, scientific notation, or more than three fractional digits, may be
+         * accepted.
          * @param ranges a list of comma-separated language ranges or a list of
          *     language ranges in the form of the "Accept-Language" header
          *     defined in <a href="https://tools.ietf.org/html/rfc2616">RFC
@@ -3360,6 +3367,11 @@ public static List<LanguageRange> parse(String ranges) {
          * This method is equivalent to
          * {@code mapEquivalents(parse(ranges), map)}.
          *
+         * @implNote This implementation interprets weights within the {@code ranges}
+         * string using {@link Double#parseDouble(String)}. As a result, some
+         * non-RFC 2616 forms of otherwise in-range values, such as leading
+         * signs, scientific notation, or more than three fractional digits, may be
+         * accepted.
          * @param ranges a list of comma-separated language ranges or a list
          *     of language ranges in the form of the "Accept-Language" header
          *     defined in <a href="https://tools.ietf.org/html/rfc2616">RFC
diff --git a/src/java.base/share/classes/sun/util/locale/LocaleMatcher.java b/src/java.base/share/classes/sun/util/locale/LocaleMatcher.java
index bc5115e1ff17b..5385a5598b68b 100644
--- a/src/java.base/share/classes/sun/util/locale/LocaleMatcher.java
+++ b/src/java.base/share/classes/sun/util/locale/LocaleMatcher.java
@@ -467,17 +467,18 @@ public static List<LanguageRange> parse(String ranges) {
                 try {
                     w = Double.parseDouble(range.substring(index));
                 }
-                catch (Exception e) {
-                    throw new IllegalArgumentException("weight=\""
+                catch (NumberFormatException _) {
+                    throw new IllegalArgumentException("The weight \""
                                   + range.substring(index)
-                                  + "\" for language range \"" + r + "\"");
+                                  + "\" for language range \"" + r + "\""
+                                  + " must be between " + MIN_WEIGHT
+                                  + " and " + MAX_WEIGHT + ", inclusive.");
                 }
-
                 if (w < MIN_WEIGHT || w > MAX_WEIGHT) {
-                    throw new IllegalArgumentException("weight=" + w
-                                  + " for language range \"" + r
-                                  + "\". It must be between " + MIN_WEIGHT
-                                  + " and " + MAX_WEIGHT + ".");
+                    throw new IllegalArgumentException("The weight \"" + w
+                                  + "\" for language range \"" + r + "\""
+                                  + " must be between " + MIN_WEIGHT
+                                  + " and " + MAX_WEIGHT + ", inclusive.");
                 }
             }
 
diff --git a/test/jdk/java/util/Locale/LocaleMatchingTest.java b/test/jdk/java/util/Locale/LocaleMatchingTest.java
index c5d8a00d45882..806229ca8eb98 100644
--- a/test/jdk/java/util/Locale/LocaleMatchingTest.java
+++ b/test/jdk/java/util/Locale/LocaleMatchingTest.java
@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 7069824 8042360 8032842 8175539 8210443 8242010 8276302 8381644
+ * @bug 7069824 8042360 8032842 8175539 8210443 8242010 8276302 8381644 8387261
  * @summary Verify implementation for Locale matching.
  * @run junit/othervm LocaleMatchingTest
  */
@@ -93,6 +93,7 @@ static Object[][] LRConstructorIAEData() {
                 {"1996-de-Latn", MAX_WEIGHT},
                 // Testcase for 8042360
                 {"en-Latn-1234567890", MAX_WEIGHT},
+                {"en", Double.NaN},
         };
     }
 
@@ -146,6 +147,7 @@ static Object[][] LRParseIAEData() {
                 // Ranges
                 {""},
                 {"ja;q=3"},
+                {"en;q=NaN"}
         };
     }