diff --git a/gmime/gmime-internal.h b/gmime/gmime-internal.h
index eff1bc6..32dc73d 100644
--- a/gmime/gmime-internal.h
+++ b/gmime/gmime-internal.h
@@ -50,6 +50,8 @@ G_GNUC_INTERNAL GMimeFormatOptions *_g_mime_format_options_clone (GMimeFormatOpt
 /* GMimeParserOptions */
 G_GNUC_INTERNAL void g_mime_parser_options_init (void);
 G_GNUC_INTERNAL void g_mime_parser_options_shutdown (void);
+G_GNUC_INTERNAL void _g_mime_parser_options_notify (GMimeParserOptions *options, GObject *object, gint64 offset,
+						    GMimeError errcode, const gchar *item);
 
 /* GMimeHeader */
 //G_GNUC_INTERNAL void _g_mime_header_set_raw_value (GMimeHeader *header, const char *raw_value);
diff --git a/gmime/gmime-param.c b/gmime/gmime-param.c
index 29b44eb..b875322 100644
--- a/gmime/gmime-param.c
+++ b/gmime/gmime-param.c
@@ -1361,24 +1361,28 @@ decode_param_list (GMimeParserOptions *options, const char *in)
 				g_free (name);
 			}
 		} else {
-			param = g_mime_param_new ();
-			param->name = name;
-			
-			if (encoded) {
-				/* singleton encoded rfc2184 param value */
-				param->value = rfc2184_decode (value, &charset, &lang);
-				param->charset = charset;
-				param->method = method;
-				param->lang = lang;
-				g_free (value);
+			if (g_mime_param_list_get_parameter(params, name) != NULL) {
+				_g_mime_parser_options_notify (options, NULL, 0U, GMIME_ERR_DUPLICATED_PARAMETER, name);
 			} else {
-				/* normal parameter value */
-				param->charset = rfc2047_charset ? g_strdup (rfc2047_charset) : NULL;
-				param->method = method;
-				param->value = value;
+				param = g_mime_param_new ();
+				param->name = name;
+
+				if (encoded) {
+					/* singleton encoded rfc2184 param value */
+					param->value = rfc2184_decode (value, &charset, &lang);
+					param->charset = charset;
+					param->method = method;
+					param->lang = lang;
+					g_free (value);
+				} else {
+					/* normal parameter value */
+					param->charset = rfc2047_charset ? g_strdup (rfc2047_charset) : NULL;
+					param->method = method;
+					param->value = value;
+				}
+
+				g_mime_param_list_add (params, param);
 			}
-			
-			g_mime_param_list_add (params, param);
 		}
 		
 		skip_cfws (&inptr);
diff --git a/gmime/gmime-parser-options.c b/gmime/gmime-parser-options.c
index 7eb05e8..025dd44 100644
--- a/gmime/gmime-parser-options.c
+++ b/gmime/gmime-parser-options.c
@@ -48,6 +48,7 @@ struct _GMimeParserOptions {
 	GMimeRfcComplianceMode rfc2047;
 	gboolean allow_no_domain;
 	char **charsets;
+	GMimeParserIssueCB issue_cb;
 };
 
 static GMimeParserOptions *default_options = NULL;
@@ -72,6 +73,14 @@ g_mime_parser_options_shutdown (void)
 	default_options = NULL;
 }
 
+void
+_g_mime_parser_options_notify (GMimeParserOptions *options, GObject *object, guint offset,
+			       guint issue, const gchar *item)
+{
+	if ((options != NULL) && (options->issue_cb != NULL)) {
+		options->issue_cb(object, offset, issue, item);
+	}
+}
 
 /**
  * g_mime_parser_options_get_default:
@@ -110,6 +119,8 @@ g_mime_parser_options_new (void)
 	options->charsets[1] = g_strdup ("iso-8859-1");
 	options->charsets[2] = NULL;
 	
+	options->issue_cb = NULL;
+
 	return options;
 }
 
@@ -145,6 +156,8 @@ g_mime_parser_options_clone (GMimeParserOptions *options)
 		clone->charsets[i] = g_strdup (options->charsets[i]);
 	clone->charsets[i] = NULL;
 	
+	clone->issue_cb = options->issue_cb;
+
 	return clone;
 }
 
@@ -393,3 +406,18 @@ g_mime_parser_options_set_fallback_charsets (GMimeParserOptions *options, const
 		options->charsets[i] = g_strdup (charsets[i]);
 	options->charsets[n] = NULL;
 }
+
+
+GMimeParserIssueCB
+g_mime_parser_options_get_issue_cb (GMimeParserOptions *options)
+{
+	return (options != NULL) ? options->issue_cb : default_options->issue_cb;
+}
+
+void
+g_mime_parser_options_set_issue_cb (GMimeParserOptions *options, GMimeParserIssueCB issue_cb)
+{
+	g_return_if_fail (options != NULL);
+
+	options->issue_cb = issue_cb;
+}
diff --git a/gmime/gmime-parser-options.h b/gmime/gmime-parser-options.h
index b5c9af7..e90c765 100644
--- a/gmime/gmime-parser-options.h
+++ b/gmime/gmime-parser-options.h
@@ -41,6 +41,11 @@ typedef enum {
 	GMIME_RFC_COMPLIANCE_STRICT
 } GMimeRfcComplianceMode;
 
+typedef enum {
+	GMIME_ERR_DUPLICATED_CONTENT_HDR = 1U,
+	GMIME_ERR_DUPLICATED_PARAMETER,
+} GMimeError;
+
 /**
  * GMimeParserOptions:
  *
@@ -48,6 +53,8 @@ typedef enum {
  **/
 typedef struct _GMimeParserOptions GMimeParserOptions;
 
+typedef void (*GMimeParserIssueCB) (GObject *object, gint64 offset, GMimeError errcode, const gchar *item);
+
 
 GType g_mime_parser_options_get_type (void);
 
@@ -73,6 +80,9 @@ void g_mime_parser_options_set_rfc2047_compliance_mode (GMimeParserOptions *opti
 const char **g_mime_parser_options_get_fallback_charsets (GMimeParserOptions *options);
 void g_mime_parser_options_set_fallback_charsets (GMimeParserOptions *options, const char **charsets);
 
+GMimeParserIssueCB g_mime_parser_options_get_issue_cb (GMimeParserOptions *options);
+void g_mime_parser_options_set_issue_cb (GMimeParserOptions *options, GMimeParserIssueCB issue_cb);
+
 G_END_DECLS
 
 #endif /* __GMIME_PARSER_OPTIONS_H__ */
diff --git a/gmime/gmime-parser.c b/gmime/gmime-parser.c
index 092279c..c6871a8 100644
--- a/gmime/gmime-parser.c
+++ b/gmime/gmime-parser.c
@@ -1671,8 +1671,13 @@ parser_scan_message_part (GMimeParser *parser, GMimeParserOptions *options, GMim
 		header = priv->headers->pdata[i];
 		
 		if (g_ascii_strncasecmp (header->name, "Content-", 8) != 0) {
-			_g_mime_object_append_header ((GMimeObject *) message, header->name, header->raw_name,
-						      header->raw_value, header->offset);
+			if (g_mime_object_get_header((GMimeObject *) message, header->name) != NULL) {
+				_g_mime_parser_options_notify (options, G_OBJECT(parser), header->offset,
+							       GMIME_ERR_DUPLICATED_CONTENT_HDR, header->name);
+			} else {
+				_g_mime_object_append_header ((GMimeObject *) message, header->name, header->raw_name,
+							      header->raw_value, header->offset);
+			}
 		}
 	}
 	
@@ -1713,8 +1718,13 @@ parser_construct_leaf_part (GMimeParser *parser, GMimeParserOptions *options, Co
 		header = priv->headers->pdata[i];
 		
 		if (!toplevel || !g_ascii_strncasecmp (header->name, "Content-", 8)) {
-			_g_mime_object_append_header (object, header->name, header->raw_name,
-						      header->raw_value, header->offset);
+			if (g_mime_object_get_header(object, header->name) != NULL) {
+				_g_mime_parser_options_notify (options, G_OBJECT(parser), header->offset,
+							       GMIME_ERR_DUPLICATED_CONTENT_HDR, header->name);
+			} else {
+				_g_mime_object_append_header (object, header->name, header->raw_name,
+							      header->raw_value, header->offset);
+			}
 		}
 	}
 	
@@ -1856,8 +1866,13 @@ parser_construct_multipart (GMimeParser *parser, GMimeParserOptions *options, Co
 		header = priv->headers->pdata[i];
 		
 		if (!toplevel || !g_ascii_strncasecmp (header->name, "Content-", 8)) {
-			_g_mime_object_append_header (object, header->name, header->raw_name,
-						      header->raw_value, header->offset);
+			if (g_mime_object_get_header(object, header->name) != NULL) {
+				_g_mime_parser_options_notify (options, G_OBJECT(parser), header->offset,
+							       GMIME_ERR_DUPLICATED_CONTENT_HDR, header->name);
+			} else {
+				_g_mime_object_append_header (object, header->name, header->raw_name,
+						      	      header->raw_value, header->offset);
+			}
 		}
 	}
 	
@@ -1981,6 +1996,7 @@ parser_construct_message (GMimeParser *parser, GMimeParserOptions *options)
 	
 	message = g_mime_message_new (FALSE);
 	((GMimeObject *) message)->ensure_newline = FALSE;
+	_g_mime_header_list_set_options(g_mime_object_get_header_list(GMIME_OBJECT(message)), options);
 	
 	for (i = 0; i < priv->headers->len; i++) {
 		header = priv->headers->pdata[i];
@@ -1996,8 +2012,13 @@ parser_construct_message (GMimeParser *parser, GMimeParserOptions *options)
 		}
 		
 		if (g_ascii_strncasecmp (header->name, "Content-", 8) != 0) {
-			_g_mime_object_append_header ((GMimeObject *) message, header->name, header->raw_name,
-						      header->raw_value, header->offset);
+			if (g_mime_object_get_header((GMimeObject *) message, header->name) != NULL) {
+				_g_mime_parser_options_notify (options, G_OBJECT(parser), header->offset,
+							       GMIME_ERR_DUPLICATED_CONTENT_HDR, header->name);
+			} else {
+				_g_mime_object_append_header ((GMimeObject *) message, header->name, header->raw_name,
+							      header->raw_value, header->offset);
+			}
 		}
 	}
 	
diff --git a/tests/test-parser.c b/tests/test-parser.c
index 94f7161..a0a25f1 100644
--- a/tests/test-parser.c
+++ b/tests/test-parser.c
@@ -154,9 +154,16 @@ print_mime_struct_iter (GMimeMessage *message)
 #endif /* PRINT_MIME_STRUCT */
 
 static void
+report_issue(GObject *object, gint64 offset, GMimeError errcode, const gchar *item)
+{
+	g_warning("%p %" G_GINT64_FORMAT " %u %s", object, offset, (unsigned) errcode, item);
+}
+
+static void
 test_parser (GMimeStream *stream)
 {
 	GMimeFormatOptions *format = g_mime_format_options_get_default ();
+	GMimeParserOptions *options;
 	GMimeParser *parser;
 	GMimeMessage *message;
 	char *text;
@@ -167,7 +174,9 @@ test_parser (GMimeStream *stream)
 	g_mime_parser_init_with_stream (parser, stream);
 	
 	ZenTimerStart (NULL);
-	message = g_mime_parser_construct_message (parser, NULL);
+	options = g_mime_parser_options_new();
+	g_mime_parser_options_set_issue_cb(options, report_issue);
+	message = g_mime_parser_construct_message (parser, options);
 	ZenTimerStop (NULL);
 	ZenTimerReport (NULL, "gmime::parser_construct_message");