diff --git a/src/cat/CommandInterface.cpp b/src/cat/CommandInterface.cpp
index 240e7e46e..3ebc795e0 100644
--- a/src/cat/CommandInterface.cpp
+++ b/src/cat/CommandInterface.cpp
@@ -96,16 +96,16 @@ int CommandInterface::GetParticleType(std::string type)
 	Element * elements = m->GetSimulation()->elements;
 
 	// alternative names for some elements
-	if (strcasecmp(txt,"C4")==0) i = PT_PLEX;
-	else if (strcasecmp(txt,"C5")==0) i = PT_C5;
-	else if (strcasecmp(txt,"NONE")==0) i = PT_NONE;
+	if (strcasecmp(txt,"C4")==0) return PT_PLEX;
+	else if (strcasecmp(txt,"C5")==0) return PT_C5;
+	else if (strcasecmp(txt,"NONE")==0) return PT_NONE;
 	for (i=1; i<PT_NUM; i++) {
 		if (strcasecmp(txt, elements[i].Name)==0 && elements[i].Enabled)
 		{
 			return i;
 		}
 	}
-	return i;
+	return -1;
 }
 
 std::string CommandInterface::GetLastError()
diff --git a/src/cat/TPTScriptInterface.cpp b/src/cat/TPTScriptInterface.cpp
index 9cfba0767..2f250a51e 100644
--- a/src/cat/TPTScriptInterface.cpp
+++ b/src/cat/TPTScriptInterface.cpp
@@ -211,9 +211,15 @@ AnyType TPTScriptInterface::tptS_set(std::deque<std::string> * words)
 	if(value.GetType() == TypeNumber)
 		newValue = ((NumberType)value).Value();
 	else if(value.GetType() == TypeString)
+	{
 		newValue = GetParticleType(((StringType)value).Value());
+		if (newValue < 0 || newValue >= PT_NUM)
+			throw GeneralException("Invalid element");
+	}
 	else
 		throw GeneralException("Invalid value for assignment");
+	if (property.Value() == "type" && (newValue < 0 || newValue >= PT_NUM))
+		throw GeneralException("Invalid element");
 
 	if(selector.GetType() == TypePoint || selector.GetType() == TypeNumber)
 	{