diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 96bda43a32..e55f28822b 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -39,7 +39,7 @@ std::ostream & operator << (std::ostream & str, const Value & v)
         str << v.path; // !!! escaping?
         break;
     case tNull:
-        str << "true";
+        str << "null";
         break;
     case tAttrs: {
         str << "{ ";
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 03bf43a3b9..c7533479aa 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -5,6 +5,7 @@
 
 #include "nixexpr.hh"
 #include "symbol-table.hh"
+#include "hash.hh"
 
 typedef union _ATermList * ATermList;
 
@@ -12,7 +13,6 @@ typedef union _ATermList * ATermList;
 namespace nix {
 
 
-class Hash;
 class EvalState;
 struct Env;
 struct Value;
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 2d26fc66da..e7c0700cf4 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -481,7 +481,16 @@ void printMsg_(Verbosity level, const format & f)
     else if (logType == ltEscapes && level != lvlInfo)
         prefix = "\033[" + escVerbosity(level) + "s";
     string s = (format("%1%%2%\n") % prefix % f.str()).str();
-    writeToStderr((const unsigned char *) s.c_str(), s.size());
+    try {
+        writeToStderr((const unsigned char *) s.c_str(), s.size());
+    } catch (SysError & e) {
+        /* Ignore failing writes to stderr if we're in an exception
+           handler, otherwise throw an exception.  We need to ignore
+           write errors in exception handlers to ensure that cleanup
+           code runs to completion if the other side of stderr has
+           been closed unexpectedly. */
+        if (!std::uncaught_exception()) throw;
+    }
 }
 
 
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index a67ce243a4..47dab0457a 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -270,7 +270,6 @@ static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
                     d = j->first.system == k->second.first.system ? 0 :
                         j->first.system == thisSystem ? 1 :
                         k->second.first.system == thisSystem ? -1 : 0;
-                    printMsg(lvlError, format("%1% %2% %3% %4%") % j->first.system % k->second.first.system % thisSystem % d);
                     if (d == 0)
                         d = comparePriorities(state, j->first, k->second.first);
                     if (d == 0)