diff --git a/opm/common/utility/parameters/ParameterGroup.cpp b/opm/common/utility/parameters/ParameterGroup.cpp
index 1afbd58b5f1..9d587cbf903 100644
--- a/opm/common/utility/parameters/ParameterGroup.cpp
+++ b/opm/common/utility/parameters/ParameterGroup.cpp
@@ -117,7 +117,7 @@ namespace Opm {
                 int commentpos = parameter.find(ID_comment);
                 if (commentpos != 0) {
                     if (commentpos != int(std::string::npos)) {
-                        parameter = parameter.substr(0, commentpos);
+                        parameter.resize(commentpos);
                     }
                     int fpos = parameter.find(ID_delimiter_assignment);
                     if (fpos == int(std::string::npos)) {
diff --git a/test_util/rewriteEclFile.cpp b/test_util/rewriteEclFile.cpp
index 2dbd58fd952..932594adbc9 100644
--- a/test_util/rewriteEclFile.cpp
+++ b/test_util/rewriteEclFile.cpp
@@ -60,7 +60,8 @@ int main(int argc, char **argv) {
     int p1 = outputFile.find_last_of(".");
     std::string ext = outputFile.substr(p1+1);
 
-    outputFile = outputFile.substr(0,p1) + "_REWRITE." + ext;
+    outputFile.resize(p1);
+    outputFile += "_REWRITE." + ext;
     Opm::EclIO::EclOutput outFile(outputFile, reffile.formattedInput());
 
     if (reffile.is_ix())