Look for blib/arch as well for FCGI.pm.

WTF is this anyway?

    PM            => {'FCGI.pm' => '$(INST_ARCHLIBDIR)/FCGI.pm'},

lib/App/cpanminus/script.pm

@@ -1406,20 +1406,36 @@ sub save_meta {
         File::Copy::copy("MYMETA.json", "$dir/MYMETA.json");
     }
 
+    my $provides = $self->_merge_hashref(
+        map Module::Metadata->package_versions_from_directory($_),
+            qw( blib/lib blib/arch ) # FCGI.pm :(
+    );
+
     my $local = {
         name => $module_name,
         module => $module,
         version => $dist->{version},
         dist => $dist->{distvname},
         pathname => $dist->{pathname},
-        provides => Module::Metadata->package_versions_from_directory("blib/lib"),
+        provides => $provides,
     };
 
     require JSON::PP;
     open my $fh, ">", "$dir/install.json" or die $!;
     print $fh JSON::PP::encode_json($local);
 }
 
+sub _merge_hashref {
+    my($self, @hashrefs) = @_;
+
+    my %hash;
+    for my $h (@hashrefs) {
+        %hash = (%hash, %$h);
+    }
+
+    return \%hash;
+}
+
 sub install_base {
     my($self, $mm_opt) = @_;
     $mm_opt =~ /INSTALL_BASE=(\S+)/ and return $1;

xt/blib_install.t

@@ -0,0 +1,19 @@
+use strict;
+use Test::More;
+use JSON;
+use Config;
+use xt::Run;
+
+my $local_lib = "$ENV{PERL_CPANM_HOME}/perl5";
+run "-L", $local_lib, "FLORA/FCGI-0.74.tar.gz";
+
+my $file = "$local_lib/lib/perl5/$Config{archname}/.meta/FCGI-0.74/install.json";
+
+open my $in, "<", $file or die $!;
+
+my $data = JSON::decode_json(join "", <$in>);
+is $data->{name}, "FCGI";
+ok exists $data->{provides}{FCGI};
+
+done_testing;
+