diff --git a/src/main/java/seedu/address/logic/parser/ThemeCommandParser.java b/src/main/java/seedu/address/logic/parser/ThemeCommandParser.java
index 67302996d3f..1ac4b4ca77e 100644
--- a/src/main/java/seedu/address/logic/parser/ThemeCommandParser.java
+++ b/src/main/java/seedu/address/logic/parser/ThemeCommandParser.java
@@ -23,7 +23,13 @@ public ThemeCommand parse(String args) throws ParseException {
                 String.format(MESSAGE_INVALID_COMMAND_FORMAT, ThemeCommand.MESSAGE_USAGE));
         }
 
-        String theme = trimmedArgs.split("\\s+")[0];
+        String[] splitArgs = trimmedArgs.split("\\s+");
+        if (splitArgs.length > 1) {
+            throw new ParseException(
+                String.format(MESSAGE_UNKNOWN_THEME, ThemeCommand.MESSAGE_USAGE));
+        }
+
+        String theme = splitArgs[0];
 
         switch(theme) {
 
diff --git a/src/test/java/seedu/address/logic/parser/ThemeCommandParserTest.java b/src/test/java/seedu/address/logic/parser/ThemeCommandParserTest.java
index 4fd91ebcb99..baba32d905e 100644
--- a/src/test/java/seedu/address/logic/parser/ThemeCommandParserTest.java
+++ b/src/test/java/seedu/address/logic/parser/ThemeCommandParserTest.java
@@ -24,6 +24,12 @@ public void parse_unknownTheme_throwsParseException() {
             ThemeCommand.MESSAGE_USAGE));
     }
 
+    @Test
+    public void parse_twoThemes_throwsParseException() {
+        assertParseFailure(parser, "blue green", String.format(MESSAGE_UNKNOWN_THEME,
+            ThemeCommand.MESSAGE_USAGE));
+    }
+
     @Test
     public void parse_validArgs_returnsThemeCommand() {
         ThemeCommand expectedThemeCommand1 =