diff --git a/javalib/src/main/scala/java/util/regex/Matcher.scala b/javalib/src/main/scala/java/util/regex/Matcher.scala
index 53f4c3a45d..7bfe84fbd2 100644
--- a/javalib/src/main/scala/java/util/regex/Matcher.scala
+++ b/javalib/src/main/scala/java/util/regex/Matcher.scala
@@ -24,6 +24,9 @@ final class Matcher private[regex] (
   private var lastMatchIsValid = false
   private var canStillFind = true
 
+  // Group count
+  private var lastGroupCount: Option[Int] = None
+
   // Append state (updated by replacement methods)
   private var appendPos: Int = 0
 
@@ -160,6 +163,7 @@ final class Matcher private[regex] (
     regexp = pattern.newJSRegExp()
     regexp.lastIndex = prevLastIndex
     lastMatch = null
+    lastGroupCount = None
     startOfGroupCache = None
     this
   }
@@ -172,7 +176,21 @@ final class Matcher private[regex] (
     lastMatch
   }
 
-  def groupCount(): Int = ensureLastMatch.length-1
+  def groupCount(): Int = {
+    if (lastMatch != null) {
+      lastMatch.length-1
+    } else {
+      lastGroupCount match {
+        case Some(n) => n
+
+        case None =>
+          val groupCountRegex = new js.RegExp("|" + pattern0.jsPattern)
+          val newGroupCount = groupCountRegex.exec("").length-1
+          lastGroupCount = Some(newGroupCount)
+          newGroupCount
+      }
+    }
+  }
 
   def start(): Int = ensureLastMatch.index
   def end(): Int = start() + group().length
@@ -198,7 +216,7 @@ final class Matcher private[regex] (
 
   // Seal the state
 
-  def toMatchResult(): MatchResult = new SealedResult(inputstr, lastMatch, pattern())
+  def toMatchResult(): MatchResult = new SealedResult(inputstr, lastMatch, pattern(), groupCount())
 
   // Other query state methods
 
@@ -249,10 +267,11 @@ object Matcher {
   }
 
   private final class SealedResult(inputstr: String,
-      lastMatch: js.RegExp.ExecResult, pattern: Pattern)
+      lastMatch: js.RegExp.ExecResult, pattern: Pattern,
+      lastGroupCount: Int)
       extends MatchResult {
 
-    def groupCount(): Int = ensureLastMatch.length-1
+    def groupCount(): Int = lastGroupCount
 
     def start(): Int = ensureLastMatch.index
     def end(): Int = start() + group().length
diff --git a/test-suite/shared/src/test/scala/org/scalajs/testsuite/javalib/util/regex/RegexMatcherTest.scala b/test-suite/shared/src/test/scala/org/scalajs/testsuite/javalib/util/regex/RegexMatcherTest.scala
index fb01d3beb2..4e487b41eb 100644
--- a/test-suite/shared/src/test/scala/org/scalajs/testsuite/javalib/util/regex/RegexMatcherTest.scala
+++ b/test-suite/shared/src/test/scala/org/scalajs/testsuite/javalib/util/regex/RegexMatcherTest.scala
@@ -102,6 +102,7 @@ class RegexMatcherTest  {
 
   def parseExpect(regex: String, str: String, pos: (Int, Int)*): Unit = {
     val matcher = Pattern.compile(regex).matcher(str)
+    assertEquals(pos.length - 1, matcher.groupCount)
     assertTrue(matcher.find())
     assertEquals(pos.length - 1, matcher.groupCount)
     var i = 0
@@ -159,6 +160,8 @@ class RegexMatcherTest  {
   }
 
   def checkGroups(matcher: Matcher, startEndMatch: (Int, Int, String)*): Unit = {
+    assertEquals(startEndMatch.size - 1, matcher.groupCount)
+
     assertTrue(matcher.find())
 
     assertEquals(startEndMatch(0)._1, matcher.start)
@@ -233,6 +236,13 @@ class RegexMatcherTest  {
     assertTrue(matcher1.matches())
     matcher1.usePattern(patternNoDots)
     assertFalse(matcher1.matches())
+
+    val patternWithOneGroup = Pattern.compile("ab(cd)efg")
+    val patternWithTwoGroups = Pattern.compile("ab(cd)(ef)g")
+    val matcher2 = patternWithOneGroup.matcher("Scala.js")
+    assertEquals(1, matcher2.groupCount())
+    matcher2.usePattern(patternWithTwoGroups)
+    assertEquals(2, matcher2.groupCount())
   }
 
   @Test def lookingAt(): Unit = {