diff --git a/doc/manual/release-notes.xml b/doc/manual/release-notes.xml
index a0b3ae68c2..463337e8d5 100644
--- a/doc/manual/release-notes.xml
+++ b/doc/manual/release-notes.xml
@@ -37,6 +37,11 @@
   <listitem><para>TODO: magic <varname>exportReferencesGraph</varname>
   attribute.</para></listitem>
 
+
+  <listitem><para>TODO: option <option>--max-silent-time</option>,
+  configuration setting
+  <literal>build-max-silent-time</literal>.</para></listitem>
+
   
 
 </itemizedlist>
diff --git a/nix.conf.example b/nix.conf.example
index 2b3b6b970f..be6a955a8d 100644
--- a/nix.conf.example
+++ b/nix.conf.example
@@ -78,6 +78,23 @@
 #build-max-jobs = 1
 
 
+### Option `build-max-silent-time'
+#
+# This option defines the maximum number of seconds that builder can
+# go without producing any data on standard output or standard error.
+# This is useful (for instance in a automated build system) to catch
+# builds that are stuck in an infinite loop, or to catch remote builds
+# that are hanging due to network problems.  It can be overriden using
+# the `--max-silent-time' command line switch.
+#
+# The value 0 means that there is no timeout.  This is also the
+# default.
+#
+# Example:
+#   build-max-silent-time = 600 # = 10 minutes
+#build-max-silent-time = 0
+
+
 ### Option `build-users-group'
 #
 # This options specifies the Unix group containing the Nix build user
diff --git a/scripts/nix-build.in b/scripts/nix-build.in
index f32b2eb35a..08201f8576 100644
--- a/scripts/nix-build.in
+++ b/scripts/nix-build.in
@@ -83,6 +83,12 @@ EOF
         $n += 2;
     }
 
+    elsif ($arg eq "--max-jobs" or $arg eq "-j" or $arg eq "--max-silent-time") {
+        $n++;
+        die "$0: `$arg' requires an argument\n" unless $n < scalar @ARGV;
+        push @buildArgs, ($arg, $ARGV[$n]);
+    }
+
     elsif (substr($arg, 0, 1) eq "-") {
         push @buildArgs, $arg;
     }
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index d7fb240192..f1a7db40dc 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -57,6 +57,18 @@ static void setLogType(string lt)
 }
 
 
+static unsigned int getIntArg(const string & opt,
+    Strings::iterator & i, const Strings::iterator & end)
+{
+    ++i;
+    if (i == end) throw UsageError(format("`%1%' requires an argument") % opt);
+    int n;
+    if (!string2Int(*i, n) || n < 0)
+        throw UsageError(format("`%1%' requires a non-negative integer") % opt);
+    return n;
+}
+
+
 struct RemoveTempRoots 
 {
     ~RemoveTempRoots()
@@ -91,12 +103,8 @@ static void initAndRun(int argc, char * * argv)
 
     /* Get some settings from the configuration file. */
     thisSystem = querySetting("system", SYSTEM);
-    {
-        int n;
-        if (!string2Int(querySetting("build-max-jobs", "1"), n) || n < 0)
-            throw Error("invalid value for configuration setting `build-max-jobs'");
-        maxBuildJobs = n;
-    }
+    maxBuildJobs = queryIntSetting("build-max-jobs", 1);
+    maxSilentTime = queryIntSetting("build-max-silent-time", 0);
 
     /* Catch SIGINT. */
     struct sigaction act, oact;
@@ -180,16 +188,12 @@ static void initAndRun(int argc, char * * argv)
             keepGoing = true;
         else if (arg == "--fallback")
             tryFallback = true;
-        else if (arg == "--max-jobs" || arg == "-j") {
-            ++i;
-            if (i == args.end()) throw UsageError("`--max-jobs' requires an argument");
-            int n;
-            if (!string2Int(*i, n) || n < 0)
-                throw UsageError(format("`--max-jobs' requires a non-negative integer"));
-            maxBuildJobs = n;
-        }
+        else if (arg == "--max-jobs" || arg == "-j")
+            maxBuildJobs = getIntArg(arg, i, args.end());
         else if (arg == "--readonly-mode")
             readOnlyMode = true;
+        else if (arg == "--max-silent-time")
+            maxSilentTime = getIntArg(arg, i, args.end());
         else remaining.push_back(arg);
     }
 
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 033cc43d9e..cff114a182 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -13,6 +13,7 @@
 #include <boost/weak_ptr.hpp>
 #include <boost/enable_shared_from_this.hpp>
 
+#include <time.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -135,6 +136,7 @@ struct Child
     WeakGoalPtr goal;
     set<int> fds;
     bool inBuildSlot;
+    time_t lastOutput; /* time we last got output on stdout/stderr */
 };
 
 typedef map<pid_t, Child> Children;
@@ -660,9 +662,18 @@ DerivationGoal::~DerivationGoal()
             worker.childTerminated(pid);
 
             if (buildUser.enabled()) {
-                /* Can't let pid's destructor do it, since it may not
-                   have the appropriate privilege (i.e., the setuid
-                   helper should do it). */
+                /* Note that we can't let pid's destructor kill the
+                   the child process, since it may not have the
+                   appropriate privilege (i.e., the setuid helper
+                   should do it).
+
+                   However, if we're using a build user, then there is
+                   a tricky race condition: if we kill the build user
+                   before the child has done its setuid() to the build
+                   user uid, then it won't be killed, and we'll
+                   potentially lock up in pid.wait().  So also send a
+                   conventional kill to the child. */
+                ::kill(-pid, SIGKILL); /* ignore the result */
                 buildUser.kill();
                 pid.wait(true);
                 assert(pid == -1);
@@ -2156,6 +2167,7 @@ void Worker::childStarted(GoalPtr goal,
     Child child;
     child.goal = goal;
     child.fds = fds;
+    child.lastOutput = time(0);
     child.inBuildSlot = inBuildSlot;
     children[pid] = child;
     if (inBuildSlot) nrChildren++;
@@ -2255,6 +2267,24 @@ void Worker::waitForInput()
        the logger pipe of a build, we assume that the builder has
        terminated. */
 
+    /* If we're monitoring for silence on stdout/stderr, sleep until
+       the first deadline for any child. */
+    struct timeval timeout;
+    if (maxSilentTime != 0) {
+        time_t oldest = 0;
+        for (Children::iterator i = children.begin();
+             i != children.end(); ++i)
+        {
+            oldest = oldest == 0 || i->second.lastOutput < oldest
+                ? i->second.lastOutput : oldest;
+        }
+        time_t now = time(0);
+        timeout.tv_sec = (time_t) (oldest + maxSilentTime) <= now ? 0 :
+            oldest + maxSilentTime - now;
+        timeout.tv_usec = 0;
+        printMsg(lvlVomit, format("sleeping %1% seconds") % timeout.tv_sec);
+    }
+
     /* Use select() to wait for the input side of any logger pipe to
        become `available'.  Note that `available' (i.e., non-blocking)
        includes EOF. */
@@ -2272,11 +2302,13 @@ void Worker::waitForInput()
         }
     }
 
-    if (select(fdMax, &fds, 0, 0, 0) == -1) {
+    if (select(fdMax, &fds, 0, 0, maxSilentTime != 0 ? &timeout : 0) == -1) {
         if (errno == EINTR) return;
         throw SysError("waiting for input");
     }
 
+    time_t now = time(0);
+
     /* Process all available file descriptors. */
     for (Children::iterator i = children.begin();
          i != children.end(); ++i)
@@ -2284,9 +2316,9 @@ void Worker::waitForInput()
         checkInterrupt();
         GoalPtr goal = i->second.goal.lock();
         assert(goal);
+        
         set<int> fds2(i->second.fds);
-        for (set<int>::iterator j = fds2.begin(); j != fds2.end(); ++j)
-        {
+        for (set<int>::iterator j = fds2.begin(); j != fds2.end(); ++j) {
             if (FD_ISSET(*j, &fds)) {
                 unsigned char buffer[4096];
                 ssize_t rd = read(*j, buffer, sizeof(buffer));
@@ -2303,9 +2335,15 @@ void Worker::waitForInput()
                         % goal->getName() % rd);
                     string data((char *) buffer, rd);
                     goal->handleChildOutput(*j, data);
+                    i->second.lastOutput = now;
                 }
             }
         }
+
+        if (maxSilentTime != 0 &&
+            now - i->second.lastOutput >= (time_t) maxSilentTime)
+            throw Error(format("%1% timed out after %2% seconds of silence")
+                % goal->getName() % maxSilentTime);
     }
 }
 
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index e8c033db2e..b0316f77c2 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -24,6 +24,7 @@ Verbosity buildVerbosity = lvlInfo;
 unsigned int maxBuildJobs = 1;
 bool readOnlyMode = false;
 string thisSystem = "unset";
+unsigned int maxSilentTime = 0;
 
 
 static bool settingsRead = false;
@@ -104,5 +105,14 @@ bool queryBoolSetting(const string & name, bool def)
         % name % v);
 }
 
+
+unsigned int queryIntSetting(const string & name, unsigned int def)
+{
+    int n;
+    if (!string2Int(querySetting(name, int2String(def)), n) || n < 0)
+        throw Error(format("configuration setting `%1%' should have an integer value") % name);
+    return n;
+}
+
  
 }
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index fbb9e19d6a..51fa685947 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -62,6 +62,11 @@ extern bool readOnlyMode;
 /* The canonical system name, as returned by config.guess. */ 
 extern string thisSystem;
 
+/* The maximum time in seconds that a builer can go without producing
+   any output on stdout/stderr before it is killed.  0 means
+   infinity. */
+extern unsigned int maxSilentTime;
+
 
 Strings querySetting(const string & name, const Strings & def);
 
@@ -69,6 +74,8 @@ string querySetting(const string & name, const string & def);
 
 bool queryBoolSetting(const string & name, bool def);
 
+unsigned int queryIntSetting(const string & name, unsigned int def);
+
     
 }