diff --git a/tool/CommandDownload.cpp b/tool/CommandDownload.cpp
index 169be24c..0dfc2588 100644
--- a/tool/CommandDownload.cpp
+++ b/tool/CommandDownload.cpp
@@ -176,8 +176,8 @@ void CommandDownload::execute(const StringVector &args)
         data.data = new uint8_t[data.data_size + 1];
 
         try {
-            data.data_size = interpretAsType(
-                    dataType, contents, data.data, data.data_size);
+            data.data_size = interpretAsType(dataType, contents, data.data,
+                    data.data_size + 1);
         } catch (SizeException &e) {
             delete [] data.data;
             throwCommandException(e.what());
@@ -197,8 +197,8 @@ void CommandDownload::execute(const StringVector &args)
         data.data = new uint8_t[data.data_size + 1];
 
         try {
-            data.data_size = interpretAsType(
-                    dataType, args[valueIndex], data.data, data.data_size);
+            data.data_size = interpretAsType(dataType, args[valueIndex],
+                    data.data, data.data_size + 1);
         } catch (SizeException &e) {
             delete [] data.data;
             throwCommandException(e.what());
diff --git a/tool/CommandRegWrite.cpp b/tool/CommandRegWrite.cpp
index d00040fa..0e12e2be 100644
--- a/tool/CommandRegWrite.cpp
+++ b/tool/CommandRegWrite.cpp
@@ -131,11 +131,11 @@ void CommandRegWrite::execute(const StringVector &args)
             io.size = 1024; // FIXME
         }
 
-        io.data = new uint8_t[io.size];
+        io.data = new uint8_t[io.size + 1];
 
         try {
             io.size = interpretAsType(
-                    dataType, args[1], io.data, io.size);
+                    dataType, args[1], io.data, io.size + 1);
         } catch (SizeException &e) {
             delete [] io.data;
             throwCommandException(e.what());
diff --git a/tool/CommandSoeWrite.cpp b/tool/CommandSoeWrite.cpp
index a96312e6..76068b71 100644
--- a/tool/CommandSoeWrite.cpp
+++ b/tool/CommandSoeWrite.cpp
@@ -149,18 +149,18 @@ void CommandSoeWrite::execute(const StringVector &args)
         memSize = dataType->byteSize;
     } else {
         // guess string type size
-        memSize = args[valueArgIndex].size() + 1;
+        memSize = args[valueArgIndex].size();
         if (!memSize) {
             err << "Empty argument not allowed.";
             throwInvalidUsageException(err);
         }
     }
 
-    ioctl.data = new uint8_t[memSize];
+    ioctl.data = new uint8_t[memSize + 1];
 
     try {
         ioctl.data_size = interpretAsType(
-                dataType, args[valueArgIndex], ioctl.data, memSize);
+                dataType, args[valueArgIndex], ioctl.data, memSize + 1);
     } catch (SizeException &e) {
         delete [] ioctl.data;
         throwCommandException(e.what());
diff --git a/tool/DataTypeHandler.cpp b/tool/DataTypeHandler.cpp
index fe37de28..048733b9 100644
--- a/tool/DataTypeHandler.cpp
+++ b/tool/DataTypeHandler.cpp
@@ -191,14 +191,14 @@ size_t DataTypeHandler::interpretAsType(
         case 0x000a: // octet_string
         case 0x000b: // unicode_string
             dataSize = str.str().size();
-            if (dataSize > targetSize) {
+            if (dataSize + 1 > targetSize) { // leave room for terminating \0
                 stringstream err;
                 err << "String too large ("
-                    << dataSize << " > " << targetSize << ")";
+                    << dataSize << " > " << targetSize - 1 << ")";
                 throw SizeException(err.str());
             }
-            //str >> (char *) target;
-            str.read((char *) target, dataSize + 1); // including \0 FIXME
+            str.read((char *) target, dataSize);
+            ((char *) target)[dataSize] = 0; // terminating \0
             break;
         case 0x0011: // double
             {