diff --git a/include/DataStructures.h b/include/DataStructures.h
index a84c32ea..a4f8e573 100644
--- a/include/DataStructures.h
+++ b/include/DataStructures.h
@@ -355,6 +355,9 @@ std::string get_input_pair_short_desc(int pair);
 /// Return the long description of an input pair key ("Molar density in mol/m^3, Temperature in K" for instance)
 std::string get_input_pair_long_desc(int pair);
 
+/// Split an input pair into parameters for the two parts that form the pair
+void split_input_pair(input_pairs pair, parameters &p1, parameters &p2);
+
 extern std::string get_mixture_binary_pair_data(const std::string &CAS1, const std::string &CAS2, const std::string &param);
 
 } /* namespace CoolProp */
diff --git a/src/CoolProp.cpp b/src/CoolProp.cpp
index 4bf25c6f..44094580 100644
--- a/src/CoolProp.cpp
+++ b/src/CoolProp.cpp
@@ -285,6 +285,20 @@ void _PropsSI_outputs(shared_ptr<AbstractState> &State,
             all_trivial_outputs = false;
         }
     }
+    // If all outputs are also inputs, never do a state update
+    bool all_outputs_in_inputs = true;
+    // Split the input pair into parameters
+    parameters p1, p2;
+    split_input_pair(input_pair, p1, p2);
+    // See if each parameter is in the output vector and is a normal type input
+    for (std::size_t j = 0; j < output_parameters.size(); ++j){
+        if (output_parameters[j].type != output_parameter::OUTPUT_TYPE_NORMAL){
+            all_outputs_in_inputs = false; break;
+        }
+        if (!(output_parameters[j].Of1 == p1 || output_parameters[j].Of1 == p2)){
+            all_outputs_in_inputs = false; break;
+        }
+    }
 
 	if (get_debug_level() > 100)
 	{
@@ -308,7 +322,7 @@ void _PropsSI_outputs(shared_ptr<AbstractState> &State,
 	// Iterate over the state variable inputs
 	for (std::size_t i = 0; i < IO.size(); ++i){
 		try{
-            if (input_pair != INPUT_PAIR_INVALID && !all_trivial_outputs){
+            if (input_pair != INPUT_PAIR_INVALID && !all_trivial_outputs && !all_outputs_in_inputs){
                 // Update the state since it is a valid set of inputs
                 State->update(input_pair, in1[i], in2[i]);
             }
@@ -321,6 +335,18 @@ void _PropsSI_outputs(shared_ptr<AbstractState> &State,
         }
 
         for (std::size_t j = 0; j < IO[i].size(); ++j){
+            // If all the outputs are inputs, there is no need for a state input
+            if (all_outputs_in_inputs){
+                if (p1 == output_parameters[j].Of1){
+                    IO[i][j] = in1[i]; success = true; continue;
+                }
+                else if (p2 == output_parameters[j].Of1){
+                    IO[i][j] = in2[i]; success = true; continue;
+                }
+                else{
+                    throw ValueError();
+                }
+            }
             try{
                 output_parameter &output = output_parameters[j];
                 switch (output.type){
@@ -357,6 +383,7 @@ void _PropsSImulti(const std::vector<std::string> &Outputs,
                    std::vector<std::vector<double> > &IO)
 {
     shared_ptr<AbstractState> State;
+    CoolProp::parameters key1, key2;
     CoolProp::input_pairs input_pair;
     std::vector<output_parameter> output_parameters;
     std::vector<double> v1, v2;
@@ -372,9 +399,7 @@ void _PropsSImulti(const std::vector<std::string> &Outputs,
 
     try{
         // Get update pair
-        CoolProp::parameters key1;
         is_valid_parameter(Name1, key1);
-        CoolProp::parameters key2;
         is_valid_parameter(Name2, key2);
         input_pair = generate_update_pair(key1, Prop1, key2, Prop2, v1, v2);
     }
diff --git a/src/DataStructures.cpp b/src/DataStructures.cpp
index 6899424b..26baa414 100644
--- a/src/DataStructures.cpp
+++ b/src/DataStructures.cpp
@@ -451,8 +451,45 @@ std::string get_input_pair_long_desc(int pair)
 {
     return input_pair_information.long_desc_map[pair];
 }
-
-
+void split_input_pair(input_pairs pair, parameters &p1, parameters &p2)
+{
+    switch(pair){
+        case QT_INPUTS: p1 = iQ; p2 = iT; break;
+        case QSmolar_INPUTS: p1 = iQ; p2 = iSmolar; break;
+        case QSmass_INPUTS: p1 = iQ; p2 = iSmass; break;
+        case HmolarQ_INPUTS: p1 = iHmolar; p2 = iQ; break;
+        case HmassQ_INPUTS: p1 = iHmass; p2 = iQ; break;
+        case PQ_INPUTS: p1 = iP; p2 = iQ; break;
+        case PT_INPUTS: p1 = iP; p2 = iT; break;
+        case DmassT_INPUTS: p1 = iDmass; p2 = iT; break;
+        case DmolarT_INPUTS: p1 = iDmolar; p2 = iT; break;
+        case HmassT_INPUTS: p1 = iHmass; p2 = iT; break;
+        case HmolarT_INPUTS: p1 = iHmolar; p2 = iT; break;
+        case SmassT_INPUTS: p1 = iSmass; p2 = iT; break;
+        case SmolarT_INPUTS: p1 = iSmolar; p2 = iT; break;
+        case TUmass_INPUTS: p1 = iT; p2 = iUmass; break;
+        case TUmolar_INPUTS: p1 = iT; p2 = iUmolar; break;
+        case DmassP_INPUTS: p1 = iDmass; p2 = iP; break;
+        case DmolarP_INPUTS: p1 = iDmolar; p2 = iP; break;
+        case HmassP_INPUTS: p1 = iHmass; p2 = iP; break;
+        case HmolarP_INPUTS: p1 = iHmolar; p2 = iP; break;
+        case PSmass_INPUTS: p1 = iP; p2 = iSmass; break;
+        case PSmolar_INPUTS: p1 = iP; p2 = iSmolar; break;
+        case PUmass_INPUTS: p1 = iP; p2 = iUmass; break;
+        case PUmolar_INPUTS: p1 = iP; p2 = iUmolar; break;
+        case DmassHmass_INPUTS: p1 = iDmass; p2 = iHmass; break;
+        case DmolarHmolar_INPUTS: p1 = iDmolar; p2 = iHmolar; break;
+        case DmassSmass_INPUTS: p1 = iDmass; p2 = iSmass; break;
+        case DmolarSmolar_INPUTS: p1 = iDmolar; p2 = iSmolar; break;
+        case DmassUmass_INPUTS: p1 = iDmass; p2 = iUmass; break;
+        case DmolarUmolar_INPUTS: p1 = iDmolar; p2 = iUmolar; break;
+        case HmassSmass_INPUTS: p1 = iHmass; p2 = iSmass;break;
+        case HmolarSmolar_INPUTS: p1 = iHmolar; p2 = iSmolar; break;
+        case SmassUmass_INPUTS: p1 = iSmass; p2 = iUmass; break;
+        case SmolarUmolar_INPUTS: p1 = iSmolar; p2 = iUmolar; break;
+        default: throw ValueError(format("Invalid input pair"));
+    }
+}
 
 } /* namespace CoolProp */