Index: t/steps/auto_jit-01.t
===================================================================
--- t/steps/auto_jit-01.t	(revision 37217)
+++ t/steps/auto_jit-01.t	(working copy)
@@ -5,7 +5,7 @@
 
 use strict;
 use warnings;
-use Test::More tests =>  50;
+use Test::More tests =>  51;
 use Carp;
 use Cwd;
 use File::Path qw( mkpath );
@@ -52,7 +52,7 @@
     my $corejitdir = File::Spec->catdir ( $jitbase, $cpuarch );
     mkpath( $corejitdir, 0, 755 ) or croak "Unable to make testing directory";
     my $corejit = File::Spec->catfile( $jitbase, $cpuarch, q{core.jit} );
-    is( $step->_check_jitcapability($corejit, $cpuarch, $osname), 0,
+    is( $step->_check_jitcapability($corejit, $cpuarch, $osname, 8), 0,
         "Got expected value for _check_jitcapability(): no core.jit case");
 
     chdir $cwd or croak "Unable to change back to starting directory";
@@ -71,7 +71,7 @@
         or croak "Unable to open handle to file for testing";
     print $FH qq{Hello, JIT\n};
     close $FH or croak "Unable to close handle to file for testing";
-    is( $step->_check_jitcapability($corejit, $cpuarch, $osname), 0,
+    is( $step->_check_jitcapability($corejit, $cpuarch, $osname, 8), 0,
         "Got expected value for _check_jitcapability(): no JIT on this architecture case");
 
     chdir $cwd or croak "Unable to change back to starting directory";
@@ -92,7 +92,7 @@
     close $FH or croak "Unable to close handle to file for testing";
     my $orig = $step->{jit_is_working};
     $step->{jit_is_working} = { $cpuarch => 1 };
-    is( $step->_check_jitcapability($corejit, $cpuarch, $osname), 1,
+    is( $step->_check_jitcapability($corejit, $cpuarch, $osname, 8), 1,
         "Got expected value for _check_jitcapability(): mock JIT case");
     $step->{jit_is_working} = $orig;
 
@@ -114,13 +114,35 @@
     close $FH or croak "Unable to close handle to file for testing";
     my $orig = $step->{jit_is_working};
     $step->{jit_is_working} = { $cpuarch => 1 };
-    is( $step->_check_jitcapability($corejit, $cpuarch, $osname), 0,
+    is( $step->_check_jitcapability($corejit, $cpuarch, $osname, 8), 0,
         "Got expected value for _check_jitcapability(): mock darwin-i386 case");
     $step->{jit_is_working} = $orig;
 
     chdir $cwd or croak "Unable to change back to starting directory";
 }
 
+{
+    my $tdir = tempdir( CLEANUP => 1 );
+    chdir $tdir or croak "Unable to change to temporary directory";
+    my $jitbase = 'foo';
+    my $cpuarch = 'i386';
+    my $osname = 'MSWin32';
+    my $corejitdir = File::Spec->catdir ( $jitbase, $cpuarch );
+    mkpath( $corejitdir, 0, 755 ) or croak "Unable to make testing directory";
+    my $corejit = File::Spec->catfile( $jitbase, $cpuarch, q{core.jit} );
+    open my $FH, '>', $corejit
+        or croak "Unable to open handle to file for testing";
+    print $FH qq{Hello, JIT\n};
+    close $FH or croak "Unable to close handle to file for testing";
+    my $orig = $step->{jit_is_working};
+    $step->{jit_is_working} = { $cpuarch => 1 };
+    is( $step->_check_jitcapability($corejit, $cpuarch, $osname, 4), 0,
+        "Got expected value for _check_jitcapability(): mock single-float");
+    $step->{jit_is_working} = $orig;
+
+    chdir $cwd or croak "Unable to change back to starting directory";
+}
+
 ########### _handle_asm() ###########
 
 {
Index: config/auto/jit.pm
===================================================================
--- config/auto/jit.pm	(revision 37217)
+++ config/auto/jit.pm	(working copy)
@@ -53,6 +53,7 @@
 
     my $cpuarch     = $conf->data->get('cpuarch');
     my $osname      = $conf->data->get('osname');
+    my $nvsize      = $conf->data->get('nvsize');
 
     my $jitbase  = $self->{jitbase_default};   # base path for jit sources
 
@@ -62,7 +63,7 @@
         if $verbose;
 
     my $jitcapable =
-        $self->_check_jitcapability($corejit, $cpuarch, $osname);
+        $self->_check_jitcapability($corejit, $cpuarch, $osname, $nvsize);
 
     my $jitarchname = "$cpuarch-$osname";
     _handle_asm( {
@@ -148,7 +149,7 @@
 
 sub _check_jitcapability {
     my $self = shift;
-    my ($corejit, $cpuarch, $osname) = @_;
+    my ($corejit, $cpuarch, $osname, $nvsize) = @_;
     my $jitcapable = 0;
     if ( -e $corejit ) {
 
@@ -162,6 +163,12 @@
             $jitcapable = 1;
         }
 
+        # Can only jit double. For long double see patch in TT #352.
+        # float not yet planned.
+        if ( $nvsize != 8 ) {
+            $jitcapable = 0;
+        }
+
         # Another exception
         if ( $cpuarch eq 'i386' && $osname eq 'darwin' ) {
             $jitcapable = 0;