diff --git a/R/RcppExports.R b/R/RcppExports.R
index fd596a079..3f76db423 100644
--- a/R/RcppExports.R
+++ b/R/RcppExports.R
@@ -75,11 +75,12 @@ rxExpandSens2_ <- function(state, s1, s2) {
 #' @param state is the state to expand
 #' @param neta is the number of etas
 #' @param pred type of prediction
+#' @param isTheta logical, is the expansion actually for thetas instead of etas
 #' @keywords internal
 #' @return String of symengine expressions to evaluate to calculate df/deta
 #' @export
-rxExpandFEta_ <- function(state, neta, pred) {
-    .Call(`_rxode2_rxExpandFEta_`, state, neta, pred)
+rxExpandFEta_ <- function(state, neta, pred, isTheta = FALSE) {
+    .Call(`_rxode2_rxExpandFEta_`, state, neta, pred, isTheta)
 }
 
 #' Rep R0 for foce
diff --git a/R/rxode2.R b/R/rxode2.R
index edcaa3822..c9f841877 100644
--- a/R/rxode2.R
+++ b/R/rxode2.R
@@ -96,7 +96,7 @@ NA_LOGICAL <- NA # nolint
 #' @includeRmd man/rmdhunks/rxode2-create-models.Rmd
 #'
 #' @includeRmd man/rmdhunks/rxode2-syntax-hunk.Rmd
-#' 
+#'
 #' @return An object (environment) of class `rxode2` (see Chambers and Temple Lang (2001))
 #'      consisting of the following list of strings and functions:
 #'
@@ -1275,6 +1275,7 @@ rxCompile <- function(model, dir, prefix, force = FALSE, modName = NULL,
       .cc <- gsub("\n", "", .cc)
       .cflags <- rawToChar(sys::exec_internal(file.path(R.home("bin"), "R"), c("CMD", "config", "CFLAGS"))$stdout)
       .cflags <- gsub("\n", "", .cflags)
+      .cflags <- paste0(.cflags, " -O", getOption("rxode2.compile.O", "2"))
       .shlibCflags <- rawToChar(sys::exec_internal(file.path(R.home("bin"), "R"), c("CMD", "config", "SHLIB_CFLAGS"))$stdout)
       .shlibCflags <- gsub("\n", "", .shlibCflags)
       .cpicflags <- rawToChar(sys::exec_internal(file.path(R.home("bin"), "R"), c("CMD", "config", "CPICFLAGS"))$stdout)
diff --git a/R/symengine.R b/R/symengine.R
index 6c56c9bca..1114b5a1f 100644
--- a/R/symengine.R
+++ b/R/symengine.R
@@ -67,7 +67,11 @@ regIfOrElse <- rex::rex(or(regIf, regElse))
   "rxGt" = c("(", ">", ")"),
   "rxLt" = c("(", "<", ")"),
   "rxAnd" = c("(", "&&", ")"),
-  "rxOr" = c("(", "||", ")")
+  "rxOr" = c("(", "||", ")"),
+  "R_pow"=c("(", ")^(", ")"),
+  "R_pow_di"=c("(", ")^(", ")"),
+  "Rx_pow"=c("(", ")^(", ")"),
+  "Rx_pow_di"=c("(", ")^(", ")")
 )
 
 ## atan2
diff --git a/inst/include/rxode2_RcppExports.h b/inst/include/rxode2_RcppExports.h
index bc88a6150..5b79439d4 100644
--- a/inst/include/rxode2_RcppExports.h
+++ b/inst/include/rxode2_RcppExports.h
@@ -89,17 +89,17 @@ namespace rxode2 {
         return Rcpp::as<List >(rcpp_result_gen);
     }
 
-    inline List rxExpandFEta_(CharacterVector state, int neta, int pred) {
-        typedef SEXP(*Ptr_rxExpandFEta_)(SEXP,SEXP,SEXP);
+    inline List rxExpandFEta_(CharacterVector state, int neta, int pred, bool isTheta = false) {
+        typedef SEXP(*Ptr_rxExpandFEta_)(SEXP,SEXP,SEXP,SEXP);
         static Ptr_rxExpandFEta_ p_rxExpandFEta_ = NULL;
         if (p_rxExpandFEta_ == NULL) {
-            validateSignature("List(*rxExpandFEta_)(CharacterVector,int,int)");
+            validateSignature("List(*rxExpandFEta_)(CharacterVector,int,int,bool)");
             p_rxExpandFEta_ = (Ptr_rxExpandFEta_)R_GetCCallable("rxode2", "_rxode2_rxExpandFEta_");
         }
         RObject rcpp_result_gen;
         {
             RNGScope RCPP_rngScope_gen;
-            rcpp_result_gen = p_rxExpandFEta_(Shield<SEXP>(Rcpp::wrap(state)), Shield<SEXP>(Rcpp::wrap(neta)), Shield<SEXP>(Rcpp::wrap(pred)));
+            rcpp_result_gen = p_rxExpandFEta_(Shield<SEXP>(Rcpp::wrap(state)), Shield<SEXP>(Rcpp::wrap(neta)), Shield<SEXP>(Rcpp::wrap(pred)), Shield<SEXP>(Rcpp::wrap(isTheta)));
         }
         if (rcpp_result_gen.inherits("interrupted-error"))
             throw Rcpp::internal::InterruptedException();
diff --git a/man/reexports.Rd b/man/reexports.Rd
index f1310e9e9..365c14ab7 100644
--- a/man/reexports.Rd
+++ b/man/reexports.Rd
@@ -82,3 +82,4 @@ below to see their documentation.
   \item{rxode2random}{\code{\link[rxode2random:dot-cbindOme]{.cbindOme}}, \code{\link[rxode2random:dot-expandPars]{.expandPars}}, \code{\link[rxode2random:dot-vecDf]{.vecDf}}, \code{\link[rxode2random]{cvPost}}, \code{\link[rxode2random]{invWR1d}}, \code{\link[rxode2random]{phi}}, \code{\link[rxode2random]{rinvchisq}}, \code{\link[rxode2random]{rLKJ1}}, \code{\link[rxode2random]{rxGetSeed}}, \code{\link[rxode2random]{rxGetSeed}}, \code{\link[rxode2random]{rxRmvn}}, \code{\link[rxode2random]{rxSeedEng}}, \code{\link[rxode2random]{rxSetSeed}}, \code{\link[rxode2random]{rxSetSeed}}, \code{\link[rxode2random]{rxSetSeed}}, \code{\link[rxode2random:rxWithSeed]{rxWithPreserveSeed}}, \code{\link[rxode2random]{rxWithSeed}}, \code{\link[rxode2random]{rxWithSeed}}}
 }}
 
+\value{ Inherited from parent routine }
diff --git a/man/rxExpandFEta_.Rd b/man/rxExpandFEta_.Rd
index 5bad0135b..6daba896a 100644
--- a/man/rxExpandFEta_.Rd
+++ b/man/rxExpandFEta_.Rd
@@ -4,7 +4,7 @@
 \alias{rxExpandFEta_}
 \title{Expand d(f)/d(eta)}
 \usage{
-rxExpandFEta_(state, neta, pred)
+rxExpandFEta_(state, neta, pred, isTheta = FALSE)
 }
 \arguments{
 \item{state}{is the state to expand}
@@ -12,6 +12,8 @@ rxExpandFEta_(state, neta, pred)
 \item{neta}{is the number of etas}
 
 \item{pred}{type of prediction}
+
+\item{isTheta}{logical, is the expansion actually for thetas instead of etas}
 }
 \value{
 String of symengine expressions to evaluate to calculate df/deta
diff --git a/man/rxode2.Rd b/man/rxode2.Rd
index b395f09e1..07f01ff6a 100644
--- a/man/rxode2.Rd
+++ b/man/rxode2.Rd
@@ -327,7 +327,7 @@ compilation model.
 
 \if{html}{\out{<div class="sourceCode">}}\preformatted{## using C compiler: ‘gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0’
 
-## rxode2 2.0.14.9000 model named rx_127860d4c6ac0b95739073c636dab49a model (ready). 
+## rxode2 2.0.14.9000 model named rx_384b8fae6af90793d54f5421bf3b0191 model (ready). 
 ## x$state: depot, center
 ## x$stateExtra: cp
 ## x$params: tka, tcl, tv, add.sd, eta.ka, eta.cl, eta.v, rxerr.cp
@@ -340,7 +340,7 @@ mod$simulationIniModel
 
 \if{html}{\out{<div class="sourceCode">}}\preformatted{## using C compiler: ‘gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0’
 
-## rxode2 2.0.14.9000 model named rx_639c5fb94c3944109ebbd131bccce512 model (ready). 
+## rxode2 2.0.14.9000 model named rx_2c6306741509f68cf54c7a56464a0a99 model (ready). 
 ## x$state: depot, center
 ## x$stateExtra: cp
 ## x$params: tka, tcl, tv, add.sd, eta.ka, eta.cl, eta.v, rxerr.cp
diff --git a/src/RcppExports.cpp b/src/RcppExports.cpp
index d89f392f3..0432f25fd 100644
--- a/src/RcppExports.cpp
+++ b/src/RcppExports.cpp
@@ -144,22 +144,23 @@ RcppExport SEXP _rxode2_rxExpandSens2_(SEXP stateSEXP, SEXP s1SEXP, SEXP s2SEXP)
     return rcpp_result_gen;
 }
 // rxExpandFEta_
-List rxExpandFEta_(CharacterVector state, int neta, int pred);
-static SEXP _rxode2_rxExpandFEta__try(SEXP stateSEXP, SEXP netaSEXP, SEXP predSEXP) {
+List rxExpandFEta_(CharacterVector state, int neta, int pred, bool isTheta);
+static SEXP _rxode2_rxExpandFEta__try(SEXP stateSEXP, SEXP netaSEXP, SEXP predSEXP, SEXP isThetaSEXP) {
 BEGIN_RCPP
     Rcpp::RObject rcpp_result_gen;
     Rcpp::traits::input_parameter< CharacterVector >::type state(stateSEXP);
     Rcpp::traits::input_parameter< int >::type neta(netaSEXP);
     Rcpp::traits::input_parameter< int >::type pred(predSEXP);
-    rcpp_result_gen = Rcpp::wrap(rxExpandFEta_(state, neta, pred));
+    Rcpp::traits::input_parameter< bool >::type isTheta(isThetaSEXP);
+    rcpp_result_gen = Rcpp::wrap(rxExpandFEta_(state, neta, pred, isTheta));
     return rcpp_result_gen;
 END_RCPP_RETURN_ERROR
 }
-RcppExport SEXP _rxode2_rxExpandFEta_(SEXP stateSEXP, SEXP netaSEXP, SEXP predSEXP) {
+RcppExport SEXP _rxode2_rxExpandFEta_(SEXP stateSEXP, SEXP netaSEXP, SEXP predSEXP, SEXP isThetaSEXP) {
     SEXP rcpp_result_gen;
     {
         Rcpp::RNGScope rcpp_rngScope_gen;
-        rcpp_result_gen = PROTECT(_rxode2_rxExpandFEta__try(stateSEXP, netaSEXP, predSEXP));
+        rcpp_result_gen = PROTECT(_rxode2_rxExpandFEta__try(stateSEXP, netaSEXP, predSEXP, isThetaSEXP));
     }
     Rboolean rcpp_isInterrupt_gen = Rf_inherits(rcpp_result_gen, "interrupted-error");
     if (rcpp_isInterrupt_gen) {
@@ -1948,7 +1949,7 @@ static int _rxode2_RcppExport_validate(const char* sig) {
         signatures.insert("List(*rxExpandGrid_)(RObject&,RObject&,RObject&)");
         signatures.insert("List(*rxExpandSens_)(CharacterVector,CharacterVector)");
         signatures.insert("List(*rxExpandSens2_)(CharacterVector,CharacterVector,CharacterVector)");
-        signatures.insert("List(*rxExpandFEta_)(CharacterVector,int,int)");
+        signatures.insert("List(*rxExpandFEta_)(CharacterVector,int,int,bool)");
         signatures.insert("std::string(*rxRepR0_)(int)");
         signatures.insert("List(*rxExpandNesting)(const RObject&,List&,bool)");
         signatures.insert("bool(*rxIs)(const RObject&,std::string)");
diff --git a/src/expandGrid.cpp b/src/expandGrid.cpp
index 73a738673..addbfe5a4 100644
--- a/src/expandGrid.cpp
+++ b/src/expandGrid.cpp
@@ -248,14 +248,17 @@ List rxExpandSens2_(CharacterVector state, CharacterVector s1, CharacterVector s
 //' @param state is the state to expand
 //' @param neta is the number of etas
 //' @param pred type of prediction
+//' @param isTheta logical, is the expansion actually for thetas instead of etas
 //' @keywords internal
 //' @return String of symengine expressions to evaluate to calculate df/deta
 //' @export
 //[[Rcpp::export]]
-List rxExpandFEta_(CharacterVector state, int neta, int pred){
+List rxExpandFEta_(CharacterVector state, int neta, int pred, bool isTheta=false){
   CharacterVector fe(neta);
   CharacterVector calcS(neta);
   int nstate = state.size();
+	std::string th = "";
+	if (isTheta) th = "TH";
   for (int i = 0; i < neta; i++){
     std::string etaN = std::to_string(i+1);
     std::string feta;
@@ -263,34 +266,34 @@ List rxExpandFEta_(CharacterVector state, int neta, int pred){
 
     switch(pred){
     case 2:
-      feta = "rx__sens_rx_pred__BY_ETA_" +
+      feta = "rx__sens_rx_pred__BY_" + th + "ETA_" +
         etaN + "___";
-      calc = "assign(\"" + feta + "\",with(.s,-D(rx_pred_, ETA_" +
+      calc = "assign(\"" + feta + "\",with(.s,-D(rx_pred_, " + th + "ETA_" +
         etaN + "_)";
       for (int j = nstate; j--;){
-        calc += "-rx__sens_" + as<std::string>(state[j]) + "_BY_ETA_" + etaN +
+        calc += "-rx__sens_" + as<std::string>(state[j]) + "_BY_" + th + "ETA_" + etaN +
           "___*D(rx_pred_,\""+ symengineRes(as<std::string>(state[j])) + "\")";
       }
       calc += "), envir=.s)";
       break;
     case 1:
-      feta = "rx__sens_rx_pred__BY_ETA_" +
+      feta = "rx__sens_rx_pred__BY_" + th + "ETA_" +
         etaN + "___";
-      calc = "assign(\"" + feta + "\",with(.s,D(rx_pred_, ETA_" +
+      calc = "assign(\"" + feta + "\",with(.s,D(rx_pred_, " + th + "ETA_" +
         etaN + "_)";
       for (int j = nstate; j--;){
-        calc += "+rx__sens_" + as<std::string>(state[j]) + "_BY_ETA_" + etaN +
+        calc += "+rx__sens_" + as<std::string>(state[j]) + "_BY_" + th + "ETA_" + etaN +
           "___*D(rx_pred_,"+ symengineRes(as<std::string>(state[j])) + ")";
       }
       calc += "), envir=.s)";
       break;
     case 0:
-      feta = "rx__sens_rx_r__BY_ETA_" +
+      feta = "rx__sens_rx_r__BY_" + th + "ETA_" +
         etaN + "___";
-      calc = "assign(\"" + feta + "\",with(.s,D(rx_r_,ETA_" +
+      calc = "assign(\"" + feta + "\",with(.s,D(rx_r_," + th +"ETA_" +
         etaN + "_)";
       for (int j = nstate; j--;){
-        calc += "+rx__sens_" + as<std::string>(state[j]) + "_BY_ETA_" + etaN +
+        calc += "+rx__sens_" + as<std::string>(state[j]) + "_BY_" + th + "ETA_" + etaN +
           "___*D(rx_r_,"+ symengineRes(as<std::string>(state[j])) + ")";
       }
       calc += "), envir=.s)";
diff --git a/src/init.c b/src/init.c
index 9b27cbca2..b76245d75 100644
--- a/src/init.c
+++ b/src/init.c
@@ -168,7 +168,7 @@ SEXP _rxode2_rxAllowUnload(SEXP);
 SEXP _rxode2_rxExpandGrid_(SEXP, SEXP, SEXP);
 SEXP _rxode2_rxExpandSens_(SEXP, SEXP);
 SEXP _rxode2_rxExpandSens2_(SEXP, SEXP, SEXP);
-SEXP _rxode2_rxExpandFEta_(SEXP, SEXP, SEXP);
+SEXP _rxode2_rxExpandFEta_(SEXP, SEXP, SEXP, SEXP);
 SEXP _rxode2_rxRepR0_(SEXP);
 SEXP _rxode2_rLKJ1(SEXP, SEXP, SEXP);
 SEXP _rxode2_rLKJcv1(SEXP, SEXP);
@@ -424,7 +424,7 @@ void R_init_rxode2(DllInfo *info){
     {"_rxode2_rxExpandGrid_", (DL_FUNC) &_rxode2_rxExpandGrid_, 3},
     {"_rxode2_rxExpandSens_", (DL_FUNC) &_rxode2_rxExpandSens_, 2},
     {"_rxode2_rxExpandSens2_",(DL_FUNC) &_rxode2_rxExpandSens2_, 3},
-    {"_rxode2_rxExpandFEta_", (DL_FUNC) &_rxode2_rxExpandFEta_, 3},
+    {"_rxode2_rxExpandFEta_", (DL_FUNC) &_rxode2_rxExpandFEta_, 4},
     {"_rxode2_rxRepR0_", (DL_FUNC) &_rxode2_rxRepR0_, 1},
     {"_rxode2_rxOptRep_", (DL_FUNC) &_rxode2_rxOptRep_, 1},
     {"_rxode2_rxSetSilentErr", (DL_FUNC) &_rxode2_rxSetSilentErr, 1},
diff --git a/src/rxData.cpp b/src/rxData.cpp
index 0f431c286..3580e868d 100644
--- a/src/rxData.cpp
+++ b/src/rxData.cpp
@@ -2486,7 +2486,7 @@ LogicalVector rxSolveFree(){
   _globals.gomega = NULL;
   if (_globals.gsigma != NULL) free(_globals.gsigma);
   _globals.gsigma = NULL;
-  
+
   _globals.zeroTheta = false;
   _globals.zeroOmega = false;
   _globals.zeroSigma = false;
diff --git a/tests/testthat/test-dsl.R b/tests/testthat/test-dsl.R
index 8e29a14cd..3edce09ba 100644
--- a/tests/testthat/test-dsl.R
+++ b/tests/testthat/test-dsl.R
@@ -553,4 +553,12 @@ rxTest({
     expect_equal(rxToSE("tad"), "(t-tlast())")
     expect_equal(rxFromSE("tlast(NaN)"), "tlast()")
   })
+
+  test_that("parsing errors", {
+
+    test <- "E0=THETA[1];\nEm=0.5;\nE50=THETA[2];\ng=2;\nv=E0+Em*t^g/(E50^g+t^g);\nrx_yj_~152;\nrx_lambda_~1;\nrx_low_~0;\nrx_hi_~1;\nrx_r_~0;\nrx_pred_~DV*v-log(1+exp(v));\n"
+
+    expect_error(rxS(test), NA)
+
+  })
 })