diff --git a/dom/base/Selection.cpp b/dom/base/Selection.cpp
index b064ec5c53a8..d91232ebd50e 100644
--- a/dom/base/Selection.cpp
+++ b/dom/base/Selection.cpp
@@ -2675,24 +2675,6 @@ Selection::CollapseToEnd(ErrorResult& aRv)
   Collapse(*container, lastRange->EndOffset(), aRv);
 }
 
-/*
- * IsCollapsed -- is the whole selection just one point, or unset?
- */
-bool
-Selection::IsCollapsed() const
-{
-  uint32_t cnt = mRanges.Length();
-  if (cnt == 0) {
-    return true;
-  }
-
-  if (cnt != 1) {
-    return false;
-  }
-
-  return mRanges[0].mRange->Collapsed();
-}
-
 /* virtual */
 bool
 Selection::Collapsed()
diff --git a/dom/base/Selection.h b/dom/base/Selection.h
index 4606b6e8bb22..1facb5c8ae70 100644
--- a/dom/base/Selection.h
+++ b/dom/base/Selection.h
@@ -174,7 +174,22 @@ public:
   nsINode*     GetFocusNode();
   uint32_t     FocusOffset();
 
-  bool IsCollapsed() const;
+  /*
+   * IsCollapsed -- is the whole selection just one point, or unset?
+   */
+  bool IsCollapsed() const
+  {
+    uint32_t cnt = mRanges.Length();
+    if (cnt == 0) {
+      return true;
+    }
+
+    if (cnt != 1) {
+      return false;
+    }
+
+    return mRanges[0].mRange->Collapsed();
+  }
 
   // *JS() methods are mapped to Selection.*().
   // They may move focus only when the range represents normal selection.