diff --git a/src/parseCmtProperties.h b/src/parseCmtProperties.h
index 357debd7e..768e7c71e 100644
--- a/src/parseCmtProperties.h
+++ b/src/parseCmtProperties.h
@@ -195,11 +195,11 @@ static inline int handleRemainingAssignmentsCalcPropComplexAssign(nodeInfo ni, c
       if (tb.lh[tb.ix] == isLHSstr ||
           tb.lh[tb.ix] == isSuppressedLHSstr) {
         D_ParseNode *xpn = d_get_child(pn, 2);
-        /* Free(v); */
         const char* v2 = (char*)rc_dup_str(xpn->start_loc.s, xpn->end);
         double d = 0.0;
         int nd = sscanf(v2, "%lf", &d);
         if (nd == 1) {
+          if (v2[0] == '-') return 1;
           if (round(d) != d) {
             errorStrAssign(v);
             return 0;
@@ -211,9 +211,6 @@ static inline int handleRemainingAssignmentsCalcPropComplexAssign(nodeInfo ni, c
               return 0;
             }
           }
-        } else {
-          errorStrAssign(v);
-          return 0;
         }
       } else if (tb.lh[tb.ix] == notLHS){
         tb.lh[tb.ix] = isLHSparam;
diff --git a/src/rxode2_df.cpp b/src/rxode2_df.cpp
index a5455094c..028336069 100644
--- a/src/rxode2_df.cpp
+++ b/src/rxode2_df.cpp
@@ -710,11 +710,18 @@ extern "C" SEXP rxode2_df(int doDose0, int doTBS) {
           if (nlhs){
             for (j = 0; j < nlhs; j++){
               if (op->lhs_str[j] == 1) {
-                dfi = INTEGER(VECTOR_ELT(df, jj));
+                // factor; from string
+                IntegerVector cur = VECTOR_ELT(df, jj);
+                CharacterVector curL = cur.attr("levels");
+                dfi = INTEGER(cur);
+                int len = curL.size();
                 if (ISNA(ind->lhs[j])) {
                   dfi[ii] = NA_INTEGER;
                 } else {
                   dfi[ii] = (int)(ind->lhs[j]);
+                  if (dfi[ii] < 1 || dfi[ii] > len) {
+                    dfi[ii] = NA_INTEGER;
+                  }
                 }
                 jj++;
               } else {
diff --git a/tests/testthat/test-lhs-str.R b/tests/testthat/test-lhs-str.R
index 1a057e01a..a3bb65a68 100644
--- a/tests/testthat/test-lhs-str.R
+++ b/tests/testthat/test-lhs-str.R
@@ -86,6 +86,10 @@ f <- function() {
   expect_error(rxode2parse('a <- "matt"; alag(a)<- 2'))
   expect_error(rxode2parse("a <- \"str\"; a(0) <- -kel"))
   expect_error(rxode2parse("a <- \"str\"; a(0) <- 1"))
+  # so that pruned expressions can work
+  expect_error(rxode2parse("a <- \"str\"; a <- 1+5"), NA)
+  expect_error(rxode2parse("a <- \"str\"; a <- -1+5"), NA)
+  expect_error(rxode2parse("a <- \"str\"; a <- +1+5"), NA)
 }
 
 test_that("test lhs string assign rxode2.syntax.allow.ini=TRUE", {
@@ -126,6 +130,47 @@ test_that("lhs solve; tests lhs assign & str equals with lhs", {
   expect_true(all(s$b[s$time >= 10] == 1))
 })
 
+test_that("out of bounds solve gives NA for factors", {
+
+  rx <- rxode2({
+    if (t < 10) {
+      a <- "<10"
+    } else {
+      a <- ">=10"
+    }
+    a <- 1-3
+    b <- 1
+    if (a == "<10") {
+      b <- 0;
+    }
+  })
+
+  e <- et(1:20)
+
+  s <-rxSolve(rx, e, returnType = "data.frame")
+
+  expect_true(all(is.na(s$a)))
+
+  rx <- rxode2({
+    if (t < 10) {
+      a <- "<10"
+    } else {
+      a <- ">=10"
+    }
+    a <- 1+20
+    b <- 1
+    if (a == "<10") {
+      b <- 0;
+    }
+  })
+
+  s <-rxSolve(rx, e, returnType = "data.frame")
+
+  expect_true(all(is.na(s$a)))
+
+
+})
+
 
 test_that("lhs solve; tests lhs levels & str equals with lhs", {