diff --git a/check/check.rb b/check/check.rb
index f664a40b..e126d420 100755
--- a/check/check.rb
+++ b/check/check.rb
@@ -696,12 +696,14 @@ def initialize
     @foldname = nil # fold name of the test
     @enabled = nil  # enabled or not
     @sources = []   # FORM sources
+    @time_dilation = nil
 
     @status = nil   # status
     @times = nil    # elapsed time (array)
   end
 
-  attr_accessor :classname, :where, :foldname, :enabled, :sources, :status, :times
+  attr_accessor :classname, :where, :foldname, :enabled, :sources, :time_dilation,
+                :status, :times
 
   # Return the description of the test.
   def desc
@@ -762,6 +764,7 @@ def make_ruby_file(filename)
         requires = nil
         pendings = nil
         prepares = nil
+        time_dilation = nil
 
         infile.each_line do |line|
           line.chop!
@@ -792,6 +795,7 @@ def make_ruby_file(filename)
               requires = nil
               pendings = nil
               prepares = nil
+              time_dilation = nil
               if skipping
                 line = ""
               else
@@ -844,6 +848,9 @@ def make_ruby_file(filename)
                 prepares = prepares.join("; ")
                 line += "def prepare; #{prepares} end; "
               end
+              if !time_dilation.nil?
+                line += "def timeout; super() * #{time_dilation} end;"
+              end
               line += "end"
             end
             level = 0
@@ -889,8 +896,19 @@ def make_ruby_file(filename)
               prepares = []
             end
             prepares << $1
-          elsif heredoc.nil? && line =~ /^\*\s*#\s*(require|prepare|pend_if)\s+(.*)/
-            # *#require/prepare/pend_if, commented out in the FORM way
+          elsif heredoc.nil? && line =~ /^\s*#\s*time_dilation\s+(.*)/
+            # #time_dilation <dilation>
+            line = ""
+            if !time_dilation.nil?
+              fatal("attempted to set time_dilation twice", inname, lineno)
+            end
+            time_dilation = $1.to_f
+            if time_dilation <= 0
+              fatal("invalid time_dilation", inname, lineno)
+            end
+            info.time_dilation = time_dilation
+          elsif heredoc.nil? && line =~ /^\*\s*#\s*(require|prepare|pend_if|time_dilation)\s+(.*)/
+            # *#require/prepare/pend_if/time_dilation, commented out in the FORM way
             line = ""
           else
             if heredoc.nil?
@@ -1462,7 +1480,7 @@ def finalize
     bar_width = 40
   end
 
-  puts("timeout: #{FormTest.cfg.timeout}s")
+  puts("default timeout: #{FormTest.cfg.timeout}s")
 
   infos.each do |info|
     (0..info.sources.length - 1).each do |i|
@@ -1470,20 +1488,24 @@ def finalize
       if !info.times.nil? && i < info.times.length
         t = info.times[i]
       end
+      timeout = FormTest.cfg.timeout
+      if !info.time_dilation.nil?
+        timeout *= info.time_dilation
+      end
       if i == 0
         puts(format("%s %s  %s %s%s",
                     lpad(info.foldname, max_foldname_width),
                     lpad("(#{info.where})", max_where_width),
                     lpad(info.status.nil? ? "UNKNOWN" : info.status, status_width),
-                    bar_str(t, FormTest.cfg.timeout, bar_width),
-                    format_time(t, FormTest.cfg.timeout)))
+                    bar_str(t, timeout, bar_width),
+                    format_time(t, timeout)))
       else
         puts(format("%s %s  %s %s%s",
                     lpad("", max_foldname_width),
                     lpad("", max_where_width),
                     lpad("", status_width),
-                    bar_str(t, FormTest.cfg.timeout, bar_width),
-                    format_time(t, FormTest.cfg.timeout)))
+                    bar_str(t, timeout, bar_width),
+                    format_time(t, timeout)))
       end
     end
   end
diff --git a/check/examples.frm b/check/examples.frm
index 2444b4e4..cd7a82ce 100644
--- a/check/examples.frm
+++ b/check/examples.frm
@@ -1905,6 +1905,7 @@ Print;
     #define LOOPS "6"
     Local F = topologies_(`LOOPS',-2,{3,},QQ,PP);
     .end
+    #time_dilation 2.0
     assert succeeded?
     assert nterms("F") == 2793
 *--#] Diagrams_4 : 
diff --git a/check/features.frm b/check/features.frm
index a8fbdd26..7379d560 100644
--- a/check/features.frm
+++ b/check/features.frm
@@ -159,6 +159,41 @@ assert result("F") =~ expr("
  x^203 - x^205 - x^206 + x^207 + x^209 + x^210
 ")
 *--#] moebius_2 :
+*--#[ moebius_3 :
+* corner cases, see #430
+#do i=1,9
+  L F`i' = moebius_(2^15-`i');
+#enddo
+#do i=1,9
+  L G`i' = moebius_(2^31-`i');
+#enddo
+P;
+.end
+#time_dilation 4.0
+assert succeeded?
+if wordsize >= 2
+  assert result("F1") =~ expr("-1")
+  assert result("F2") =~ expr("1")
+  assert result("F3") =~ expr("1")
+  assert result("F4") =~ expr("0")
+  assert result("F5") =~ expr("-1")
+  assert result("F6") =~ expr("1")
+  assert result("F7") =~ expr("0")
+  assert result("F8") =~ expr("0")
+  assert result("F9") =~ expr("-1")
+end
+if wordsize >= 4
+  assert result("G1") =~ expr("-1")
+  assert result("G2") =~ expr("0")
+  assert result("G3") =~ expr("-1")
+  assert result("G4") =~ expr("0")
+  assert result("G5") =~ expr("1")
+  assert result("G6") =~ expr("-1")
+  assert result("G7") =~ expr("1")
+  assert result("G8") =~ expr("0")
+  assert result("G9") =~ expr("-1")
+end
+*--#] moebius_3 :
 *--#[ partitions_ :
 * Test partitions function
 #-
diff --git a/check/fixes.frm b/check/fixes.frm
index 568086e7..ed00e021 100644
--- a/check/fixes.frm
+++ b/check/fixes.frm
@@ -1474,6 +1474,7 @@ P;
 .end
 # Too slow on Travis CI. ParFORM didn't have this bug.
 #pend_if travis? && (!linux? || valgrind? || mpi?)
+#time_dilation 2.0
 assert succeeded?
 assert result("F1") =~ expr("2027025")
 *--#] Issue154 :