diff --git a/xpcom/string/public/nsTString.h b/xpcom/string/public/nsTString.h
index 08c0997f6a7..57b9e9307b2 100644
--- a/xpcom/string/public/nsTString.h
+++ b/xpcom/string/public/nsTString.h
@@ -410,6 +410,8 @@ class nsTString_CharT : public nsTSubstring_CharT
          * Append the given float to this string 
          */
 
+      NS_COM void AppendFloat( float aFloat );
+
       NS_COM void AppendFloat( double aFloat );
 
 #endif // !MOZ_STRING_WITH_OBSOLETE_API
diff --git a/xpcom/string/src/nsStringObsolete.cpp b/xpcom/string/src/nsStringObsolete.cpp
index 31752f66182..9dd13d7e6a7 100644
--- a/xpcom/string/src/nsStringObsolete.cpp
+++ b/xpcom/string/src/nsStringObsolete.cpp
@@ -1261,7 +1261,7 @@ nsString::AppendInt( PRInt64 aInteger, PRInt32 aRadix )
    */
 
 void
-nsCString::AppendFloat( double aFloat )
+nsCString::AppendFloat( float aFloat )
   {
     char buf[40];
     // Use Modified_cnvtf, which is locale-insensitive, instead of the
@@ -1271,7 +1271,7 @@ nsCString::AppendFloat( double aFloat )
   }
 
 void
-nsString::AppendFloat( double aFloat )
+nsString::AppendFloat( float aFloat )
   {
     char buf[40];
     // Use Modified_cnvtf, which is locale-insensitive, instead of the
@@ -1280,4 +1280,24 @@ nsString::AppendFloat( double aFloat )
     AppendWithConversion(buf);
   }
 
+void
+nsCString::AppendFloat( double aFloat )
+  {
+    char buf[40];
+    // Use Modified_cnvtf, which is locale-insensitive, instead of the
+    // locale-sensitive PR_snprintf or sprintf(3)
+    Modified_cnvtf(buf, sizeof(buf), 15, aFloat);
+    Append(buf);
+  }
+
+void
+nsString::AppendFloat( double aFloat )
+  {
+    char buf[40];
+    // Use Modified_cnvtf, which is locale-insensitive, instead of the
+    // locale-sensitive PR_snprintf or sprintf(3)
+    Modified_cnvtf(buf, sizeof(buf), 15, aFloat);
+    AppendWithConversion(buf);
+  }
+
 #endif // !MOZ_STRING_WITH_OBSOLETE_API
diff --git a/xpcom/tests/TestStrings.cpp b/xpcom/tests/TestStrings.cpp
index fedf12f33eb..8ece2656372 100644
--- a/xpcom/tests/TestStrings.cpp
+++ b/xpcom/tests/TestStrings.cpp
@@ -513,6 +513,32 @@ PRBool test_appendint64()
     }
 
 
+    return PR_TRUE;
+  }
+
+PRBool test_appendfloat()
+  {
+    nsCString str;
+    double bigdouble = 11223344556.66;
+    static const char double_expected[] = "11223344556.66";
+    static const char float_expected[] = "0.01";
+
+    // AppendFloat is used to append doubles, therefore the precision must be
+    // large enough (see bug 327719)
+    str.AppendFloat( bigdouble );
+    if (!str.Equals(double_expected)) {
+      fprintf(stderr, "Error appending a big double: Got %s\n", str.get());
+      return PR_FALSE;
+    }
+    
+    str.Truncate();
+    // AppendFloat is used to append floats (bug 327719 #27)
+    str.AppendFloat( 0.1f * 0.1f );
+    if (!str.Equals(float_expected)) {
+      fprintf(stderr, "Error appending a float: Got %s\n", str.get());
+      return PR_FALSE;
+    }
+
     return PR_TRUE;
   }
 
@@ -710,6 +736,7 @@ tests[] =
     { "test_set_length", test_set_length },
     { "test_substring", test_substring },
     { "test_appendint64", test_appendint64 },
+    { "test_appendfloat", test_appendfloat },
     { "test_findcharinset", test_findcharinset },
     { "test_rfindcharinset", test_rfindcharinset },
     { "test_stringbuffer", test_stringbuffer },