diff --git a/js/src/jsfile.c b/js/src/jsfile.c
index 52ce1cc663f..d03f7b724cd 100644
--- a/js/src/jsfile.c
+++ b/js/src/jsfile.c
@@ -273,7 +273,7 @@ js_isAbsolute(const char *name)
 }
 
 /*
- * Concatinates base and name to produce a valid filename.
+ * Concatenates base and name to produce a valid filename.
  * Returned string must be freed.
 */
 static char*
diff --git a/xpcom/io/nsIMultiplexInputStream.idl b/xpcom/io/nsIMultiplexInputStream.idl
index ec309ecd8ef..c0fc3b991f6 100644
--- a/xpcom/io/nsIMultiplexInputStream.idl
+++ b/xpcom/io/nsIMultiplexInputStream.idl
@@ -39,7 +39,7 @@
 #include "nsIInputStream.idl"
 
 /**
- * The multiplex stream concatinates a list of input streams into a single
+ * The multiplex stream concatenates a list of input streams into a single
  * stream.
  */
 
diff --git a/xpcom/io/nsMultiplexInputStream.h b/xpcom/io/nsMultiplexInputStream.h
index 32d3026de84..ac31b4d0462 100644
--- a/xpcom/io/nsMultiplexInputStream.h
+++ b/xpcom/io/nsMultiplexInputStream.h
@@ -37,7 +37,7 @@
  * ***** END LICENSE BLOCK ***** */
 
 /**
- * The multiplex stream concatinates a list of input streams into a single
+ * The multiplex stream concatenates a list of input streams into a single
  * stream.
  */