diff --git a/public/fpdf_annot.h b/public/fpdf_annot.h
index b927638..1fbc366 100644
--- a/public/fpdf_annot.h
+++ b/public/fpdf_annot.h
@@ -343,7 +343,7 @@
 // Check if |annot|'s dictionary has |key| as a key.
 //
 //   annot  - handle to an annotation.
-//   key    - the key to look for.
+//   key    - the key to look for, encoded in UTF-8.
 //
 // Returns true if |key| exists.
 FPDF_EXPORT FPDF_BOOL FPDF_CALLCONV FPDFAnnot_HasKey(FPDF_ANNOTATION annot,
@@ -353,7 +353,7 @@
 // Get the type of the value corresponding to |key| in |annot|'s dictionary.
 //
 //   annot  - handle to an annotation.
-//   key    - the key to look for.
+//   key    - the key to look for, encoded in UTF-8.
 //
 // Returns the type of the dictionary value.
 FPDF_EXPORT FPDF_OBJECT_TYPE FPDF_CALLCONV
@@ -365,7 +365,7 @@
 // FPDF_OBJECT_STRING after this function call succeeds.
 //
 //   annot  - handle to an annotation.
-//   key    - the key to the dictionary entry to be set, encoded in UTF16-LE.
+//   key    - the key to the dictionary entry to be set, encoded in UTF-8.
 //   value  - the string value to be set, encoded in UTF16-LE.
 //
 // Returns true if successful.
@@ -384,7 +384,7 @@
 // be added to |buffer| and the return value would be 0.
 //
 //   annot  - handle to an annotation.
-//   key    - the key to the requested dictionary entry.
+//   key    - the key to the requested dictionary entry, encoded in UTF-8.
 //   buffer - buffer for holding the value string, encoded in UTF16-LE.
 //   buflen - length of the buffer.
 //
@@ -402,7 +402,7 @@
 // longer needed.
 //
 //   annot  - handle to an annotation.
-//   key    - the key to the requested dictionary entry.
+//   key    - the key to the requested dictionary entry, encoded in UTF-8.
 //
 // Returns a handle to the linked annotation object, or NULL on failure.
 FPDF_EXPORT FPDF_ANNOTATION FPDF_CALLCONV
diff --git a/public/fpdf_attachment.h b/public/fpdf_attachment.h
index 411ee21..7b55974 100644
--- a/public/fpdf_attachment.h
+++ b/public/fpdf_attachment.h
@@ -77,7 +77,7 @@
 // Check if the params dictionary of |attachment| has |key| as a key.
 //
 //   attachment - handle to an attachment.
-//   key        - the key to look for.
+//   key        - the key to look for, encoded in UTF-8.
 //
 // Returns true if |key| exists.
 FPDF_EXPORT FPDF_BOOL FPDF_CALLCONV
@@ -88,7 +88,7 @@
 // the embedded |attachment|.
 //
 //   attachment - handle to an attachment.
-//   key        - the key to look for.
+//   key        - the key to look for, encoded in UTF-8.
 //
 // Returns the type of the dictionary value.
 FPDF_EXPORT FPDF_OBJECT_TYPE FPDF_CALLCONV
@@ -100,7 +100,7 @@
 // type should be FPDF_OBJECT_STRING after this function call succeeds.
 //
 //   attachment - handle to an attachment.
-//   key        - the key to the dictionary entry, encoded in UTF16-LE.
+//   key        - the key to the dictionary entry, encoded in UTF-8.
 //   value      - the string value to be set, encoded in UTF16-LE.
 //
 // Returns true if successful.
@@ -120,7 +120,7 @@
 // and the return value would be 0.
 //
 //   attachment - handle to an attachment.
-//   key        - the key to the requested string value.
+//   key        - the key to the requested string value, encoded in UTF-8.
 //   buffer     - buffer for holding the string value encoded in UTF16-LE.
 //   buflen     - length of the buffer.
 //
diff --git a/public/fpdfview.h b/public/fpdfview.h
index 3f18033..370b84e 100644
--- a/public/fpdfview.h
+++ b/public/fpdfview.h
@@ -1012,7 +1012,8 @@
 //          be of type "name".
 // Parameters:
 //          document    -   Handle to the loaded document.
-//          key         -   Name of the key in the viewer pref dictionary.
+//          key         -   Name of the key in the viewer pref dictionary,
+//                          encoded in UTF-8.
 //          buffer      -   A string to write the contents of the key to.
 //          length      -   Length of the buffer.
 // Return value: