diff --git a/src/thermo/Phase.cpp b/src/thermo/Phase.cpp
index 81b748071a..4981835d69 100644
--- a/src/thermo/Phase.cpp
+++ b/src/thermo/Phase.cpp
@@ -705,12 +705,14 @@ size_t Phase::addElement(const std::string& symbol, doublereal weight,
                          int elem_type)
 {
     // Look up the atomic weight if not given
-    if (weight == -12345.0) {
-        weight = getElementWeight(symbol);
-        if (weight < 0.0) {
-            throw CanteraError("Phase::addElement",
-                               "No atomic weight found for element: " + symbol);
+    if (weight == 0.0) {
+        try {
+            weight = getElementWeight(symbol);
+        } catch (CanteraError&) {
+            // assume this is just a custom element with zero atomic weight
         }
+    } else if (weight == -12345.0) {
+        weight = getElementWeight(symbol);
     }
 
     // Check for duplicates
diff --git a/src/thermo/ThermoFactory.cpp b/src/thermo/ThermoFactory.cpp
index 1b8d7401bd..babcad8011 100644
--- a/src/thermo/ThermoFactory.cpp
+++ b/src/thermo/ThermoFactory.cpp
@@ -474,11 +474,7 @@ void installElements(Phase& th, const XML_Node& phaseNode)
                 entropy298 = fpValueCheck(e298Node["value"]);
             }
         }
-        if (weight != 0.0) {
-            th.addElement(symbol, weight, anum, entropy298);
-        } else {
-            th.addElement(symbol);
-        }
+        th.addElement(symbol, weight, anum, entropy298);
     }
 }