diff --git a/CHANGES b/CHANGES
index 75e8da5ca..ea1301c7c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -18,6 +18,8 @@ Bugs fixed
 
 * LaTeX: Remove extraneous space after author names on PDF title page (refs: #6004)
 * #6026: LaTeX: A cross reference to definition list does not work
+* #6046: LaTeX: ``TypeError`` is raised when invalid latex_elements given
+* #6019: imgconverter: Including multipage PDF fails
 
 Testing
 --------
diff --git a/sphinx/builders/latex/__init__.py b/sphinx/builders/latex/__init__.py
index 3aba09b08..4ab408064 100644
--- a/sphinx/builders/latex/__init__.py
+++ b/sphinx/builders/latex/__init__.py
@@ -376,7 +376,7 @@ def validate_config_values(app, config):
     for key in list(config.latex_elements):
         if key not in DEFAULT_SETTINGS:
             msg = __("Unknown configure key: latex_elements[%r]. ignored.")
-            logger.warning(msg % key)
+            logger.warning(msg % (key,))
             config.latex_elements.pop(key)
 
 
diff --git a/sphinx/ext/imgconverter.py b/sphinx/ext/imgconverter.py
index 79755d351..b0b379936 100644
--- a/sphinx/ext/imgconverter.py
+++ b/sphinx/ext/imgconverter.py
@@ -66,9 +66,9 @@ class ImagemagickConverter(ImageConverter):
         # type: (unicode, unicode) -> bool
         """Converts the image to expected one."""
         try:
-            if _from.lower().endswith('.gif'):
-                # when target is GIF format, pick the first frame
-                _from += '[0]'
+            # append an index 0 to source filename to pick up the first frame
+            # (or first page) of image (ex. Animation GIF, PDF)
+            _from += '[0]'
 
             args = ([self.config.image_converter] +
                     self.config.image_converter_args +