diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index 34bb961da0..cc1c3515b8 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -2288,10 +2288,13 @@ struct GameSettingsWindow : Window {
 				/* Show the correct currency-translated value */
 				if (sd->flags & SF_GUI_CURRENCY) value64 *= _currency->rate;
 
+				CharSetFilter charset_filter = CS_NUMERAL; //default, only numeric input allowed
+				if (sd->min < 0) charset_filter = CS_NUMERAL_SIGNED; // special case, also allow '-' sign for negative input
+
 				this->valuewindow_entry = pe;
 				SetDParam(0, value64);
 				/* Limit string length to 14 so that MAX_INT32 * max currency rate doesn't exceed MAX_INT64. */
-				ShowQueryString(STR_JUST_INT, STR_CONFIG_SETTING_QUERY_CAPTION, 15, this, CS_NUMERAL, QSF_ENABLE_DEFAULT);
+				ShowQueryString(STR_JUST_INT, STR_CONFIG_SETTING_QUERY_CAPTION, 15, this, charset_filter, QSF_ENABLE_DEFAULT);
 			}
 			this->SetDisplayedHelpText(pe);
 		}
diff --git a/src/string.cpp b/src/string.cpp
index aeac4fe84f..2e14b4208e 100644
--- a/src/string.cpp
+++ b/src/string.cpp
@@ -494,11 +494,12 @@ bool strtolower(std::string &str, std::string::size_type offs)
 bool IsValidChar(WChar key, CharSetFilter afilter)
 {
 	switch (afilter) {
-		case CS_ALPHANUMERAL:  return IsPrintable(key);
-		case CS_NUMERAL:       return (key >= '0' && key <= '9');
-		case CS_NUMERAL_SPACE: return (key >= '0' && key <= '9') || key == ' ';
-		case CS_ALPHA:         return IsPrintable(key) && !(key >= '0' && key <= '9');
-		case CS_HEXADECIMAL:   return (key >= '0' && key <= '9') || (key >= 'a' && key <= 'f') || (key >= 'A' && key <= 'F');
+		case CS_ALPHANUMERAL:   return IsPrintable(key);
+		case CS_NUMERAL:        return (key >= '0' && key <= '9');
+		case CS_NUMERAL_SPACE:  return (key >= '0' && key <= '9') || key == ' ';
+		case CS_NUMERAL_SIGNED: return (key >= '0' && key <= '9') || key == '-';
+		case CS_ALPHA:          return IsPrintable(key) && !(key >= '0' && key <= '9');
+		case CS_HEXADECIMAL:    return (key >= '0' && key <= '9') || (key >= 'a' && key <= 'f') || (key >= 'A' && key <= 'F');
 		default: NOT_REACHED();
 	}
 }
diff --git a/src/string_type.h b/src/string_type.h
index 25ea65598e..b8705e403f 100644
--- a/src/string_type.h
+++ b/src/string_type.h
@@ -27,6 +27,7 @@ enum CharSetFilter {
 	CS_ALPHANUMERAL,      ///< Both numeric and alphabetic and spaces and stuff
 	CS_NUMERAL,           ///< Only numeric ones
 	CS_NUMERAL_SPACE,     ///< Only numbers and spaces
+	CS_NUMERAL_SIGNED,    ///< Only numbers and '-' for negative values
 	CS_ALPHA,             ///< Only alphabetic values
 	CS_HEXADECIMAL,       ///< Only hexadecimal characters
 };