diff --git a/pvDataApp/factory/FieldCreateFactory.cpp b/pvDataApp/factory/FieldCreateFactory.cpp
index 7024cd7..e8444ba 100644
--- a/pvDataApp/factory/FieldCreateFactory.cpp
+++ b/pvDataApp/factory/FieldCreateFactory.cpp
@@ -66,7 +66,11 @@ struct StructureArrayHashFunction {
 
 
 Scalar::Scalar(ScalarType scalarType)
-       : Field(scalar),scalarType(scalarType){}
+       : Field(scalar),scalarType(scalarType)
+{
+    if(scalarType<pvBoolean || scalarType>pvString)
+        throw std::invalid_argument("Can't construct Scalar from invalid ScalarType");
+}
 
 Scalar::~Scalar(){}
 
@@ -166,7 +170,11 @@ static StructureConstPtr deserializeStructureField(const FieldCreate* fieldCreat
 }
 
 ScalarArray::ScalarArray(ScalarType elementType)
-: Field(scalarArray),elementType(elementType){}
+: Field(scalarArray),elementType(elementType)
+{
+    if(elementType<pvBoolean || elementType>pvString)
+        throw std::invalid_argument("Can't construct ScalarArray from invalid ScalarType");
+}
 
 ScalarArray::~ScalarArray() {}
 
@@ -275,10 +283,12 @@ Structure::Structure (
     }
     size_t number = fields.size();
     for(size_t i=0; i<number; i++) {
-        String name = fieldNames[i];
-        if(name.size()<1) {
+        const String& name = fieldNames[i];
+        if(name.empty()) {
             throw std::invalid_argument("fieldNames has a zero length string");
         }
+        if(fields[i].get()==NULL)
+            throw std::invalid_argument("Can't construct Structure with NULL Field");
         // look for duplicates
         for(size_t j=i+1; j<number; j++) {
             String otherName = fieldNames[j];
diff --git a/pvDataApp/factory/TypeFunc.cpp b/pvDataApp/factory/TypeFunc.cpp
index 0d38b6c..2fa0872 100644
--- a/pvDataApp/factory/TypeFunc.cpp
+++ b/pvDataApp/factory/TypeFunc.cpp
@@ -61,7 +61,7 @@ namespace ScalarTypeFunc {
         "ubyte", "ushort", "uint", "ulong",
         "float", "double", "string",
     };
-    ScalarType getScalarType(String pvalue) {
+    ScalarType getScalarType(const String& pvalue) {
         for(size_t i=0; i<NELEMENTS(names); i++)
             if(pvalue==names[i])
                 return ScalarType(i);
diff --git a/pvDataApp/pv/pvIntrospect.h b/pvDataApp/pv/pvIntrospect.h
index 51d1015..f1df915 100644
--- a/pvDataApp/pv/pvIntrospect.h
+++ b/pvDataApp/pv/pvIntrospect.h
@@ -443,7 +443,7 @@ public:
      * @param fieldIndex The index of the desired field.
      * @return The fieldName.
      */
-    String getFieldName(std::size_t fieldIndex){return fieldNames[fieldIndex];}
+    String getFieldName(std::size_t fieldIndex) const {return fieldNames[fieldIndex];}
     /**
      * Convert the structure to a string and add it to builder.
      * @param  builder The string builder.