--- pdns-recursor-3.5.3/misc.cc
+++ pdns-recursor-3.5.3/misc.cc
@@ -22,6 +22,7 @@
 #include <netdb.h>
 #include <sys/time.h>
 #include <time.h>
+#include <sys/resource.h>
 #include <netinet/in.h>
 #include <unistd.h>
 #endif // WIN32
@@ -697,3 +698,22 @@
   } while(!strchr(buffer, '\n'));
   return true;
 }
+
+unsigned int getFilenumLimit(bool hardOrSoft)
+{
+  struct rlimit rlim;
+  if(getrlimit(RLIMIT_NOFILE, &rlim) < 0)
+    unixDie("Requesting number of available file descriptors");
+  return hardOrSoft ? rlim.rlim_max : rlim.rlim_cur;
+}
+
+void setFilenumLimit(unsigned int lim)
+{
+  struct rlimit rlim;
+
+  if(getrlimit(RLIMIT_NOFILE, &rlim) < 0)
+    unixDie("Requesting number of available file descriptors");
+  rlim.rlim_cur=lim;
+  if(setrlimit(RLIMIT_NOFILE, &rlim) < 0)
+    unixDie("Setting number of available file descriptors");
+}
--- pdns-recursor-3.5.3/misc.hh
+++ pdns-recursor-3.5.3/misc.hh
@@ -445,4 +445,6 @@
   regex_t d_preg;
 };
 
+unsigned int getFilenumLimit(bool hardOrSoft=0);
+void setFilenumLimit(unsigned int lim);
 #endif
--- pdns-recursor-3.5.3/pdns_recursor.cc
+++ pdns-recursor-3.5.3/pdns_recursor.cc
@@ -1740,7 +1740,21 @@
   
   g_tcpTimeout=::arg().asNum("client-tcp-timeout");
   g_maxTCPPerClient=::arg().asNum("max-tcp-per-client");
-  g_maxMThreads=::arg().asNum("max-mthreads");
+  g_maxMThreads=::arg().asNum("max-mthreads");	
+  unsigned int availFDs=getFilenumLimit();
+  if(g_maxMThreads * g_numThreads > availFDs) {
+    if(getFilenumLimit(true) >= g_maxMThreads * g_numThreads) {
+      setFilenumLimit(g_maxMThreads * g_numThreads);
+      L<<Logger::Warning<<"Raised soft limit on number of filedescriptors to "<<g_maxMThreads * g_numThreads<<" to match max-mthreads and threads settings"<<endl;
+    }
+    else {
+      int newval = getFilenumLimit(true) / g_numThreads;
+      L<<Logger::Warning<<"Insufficient number of filedescriptors available for max-mthreads*threads setting! ("<<availFDs<<" < "<<g_maxMThreads*g_numThreads<<"), reducing max-mthreads to "<<newval<<endl;
+      g_maxMThreads = newval;
+    }
+
+    
+  }
 
   if(g_numThreads == 1) {
     L<<Logger::Warning<<"Operating unthreaded"<<endl;