Index: src/screenshot.cpp
===================================================================
--- src/screenshot.cpp	(revision 10111)
+++ src/screenshot.cpp	(working copy)
@@ -505,6 +505,17 @@
 		GetString(_screenshot_name, STR_4004, lastof(_screenshot_name));
 	}
 
+	char invalid[] = ":/\\*?";
+	for (uint i = 0; i < sizeof(_screenshot_name); i++) {
+		for (uint j = 0; j < 5; j++) {
+			if (_screenshot_name[i] == invalid[j]) {
+				_screenshot_name[i] = '_';
+				break;
+			}
+			if (_screenshot_name[i] == '_') break;
+		}
+	}
+
 	base = strchr(_screenshot_name, 0);
 	base[0] = '.'; strcpy(base + 1, ext);
 
Index: src/misc_gui.cpp
===================================================================
--- src/misc_gui.cpp	(revision 10111)
+++ src/misc_gui.cpp	(working copy)
@@ -1396,6 +1415,17 @@
 	SetDParam(1, p->name_2);
 	SetDParam(2, _date);
 	GetString(_edit_str_buf, STR_4004, lastof(_edit_str_buf));
+
+	char invalid[] = ":/\\*?";
+	for (uint i = 0; i < sizeof(_edit_str_buf); i++) {
+		for (uint j = 0; j < 5; j++) {
+			if (_edit_str_buf[i] == invalid[j]) {
+				_edit_str_buf[i] = '_';
+				break;
+			}
+			if (_edit_str_buf[i] == '_') break;
+		}
+	}
 }
 
 extern void StartupEngines();