diff --git a/lib/Test/MockFile.pm b/lib/Test/MockFile.pm
index e9c0380..e2c27da 100644
--- a/lib/Test/MockFile.pm
+++ b/lib/Test/MockFile.pm
@@ -56,6 +56,10 @@ our $VERSION = '0.038';
 
 our %files_being_mocked;
 
+# Reverse lookup: stringified filehandle => absolute path.
+# Turns _fh_to_file from O(n) iteration to O(1) hash lookup.
+our %_fh_to_path;
+
 # Original Cwd functions saved before override
 my $_original_cwd_abs_path;
 
@@ -1729,26 +1733,8 @@ sub _fh_to_file {
 
     return unless defined $fh && length $fh;
 
-    # See if $fh is a file handle. It might be a path.
-    foreach my $path ( sort keys %files_being_mocked ) {
-        my $mock = $files_being_mocked{$path};
-
-        # Check file handles (multiple handles per file)
-        my $fhs = $mock->{'fhs'};
-        if ( $fhs && @{$fhs} ) {
-            @{$fhs} = grep { defined $_ } @{$fhs};
-            foreach my $mock_fh ( @{$fhs} ) {
-                return $path if "$mock_fh" eq "$fh";
-            }
-        }
-
-        # Check dir handle (stored as stringified handle)
-        if ( $mock->{'fh'} && $mock->{'fh'} eq "$fh" ) {
-            return $path;
-        }
-    }
-
-    return;
+    # O(1) reverse lookup instead of iterating all mocked files.
+    return $_fh_to_path{"$fh"};
 }
 
 sub _files_in_dir {
@@ -1951,6 +1937,14 @@ sub DESTROY {
         delete $self->{'_autovivified_children'};
     }
 
+    # Clean up reverse fh-to-path lookup entries for this mock's handles.
+    if ( my $fhs = $self->{'fhs'} ) {
+        for my $fh ( @{$fhs} ) {
+            delete $_fh_to_path{"$fh"} if defined $fh;
+        }
+    }
+    delete $_fh_to_path{ $self->{'fh'} } if $self->{'fh'};
+
     # If the object survives into global destruction, the object which is
     # the value of $files_being_mocked{$path} might destroy early.
     # As a result, don't worry about the self == check just delete the key.
@@ -2733,6 +2727,12 @@ sub _io_file_mock_open {
     $mock_file->{'fh'} = $fh;
     Scalar::Util::weaken( $mock_file->{'fh'} ) if ref $fh;
 
+    # Register in reverse lookup for O(1) _fh_to_file resolution.
+    $_fh_to_path{"$fh"} = $abs_path;
+    if ( ref $fh && tied( *{$fh} ) ) {
+        tied( *{$fh} )->{'_fh_string'} = "$fh";
+    }
+
     # Handle append/truncate modes
     if ( $mode eq '>>' or $mode eq '+>>' ) {
         $mock_file->{'contents'} //= '';
@@ -3079,6 +3079,12 @@ sub __open (*;$@) {
     push @{ $mock_file->{'fhs'} }, $_[0];
     Scalar::Util::weaken( $mock_file->{'fhs'}[-1] ) if ref $_[0];
 
+    # Register in reverse lookup for O(1) _fh_to_file resolution.
+    $_fh_to_path{"$_[0]"} = $mock_file->{'path'};
+    if ( ref $_[0] && tied( *{ $_[0] } ) ) {
+        tied( *{ $_[0] } )->{'_fh_string'} = "$_[0]";
+    }
+
     # Fix tell based on open options.
     # Track whether this open creates the file (transitions from non-existent).
     my $was_new = !defined $mock_file->{'contents'};
@@ -3275,6 +3281,12 @@ sub __sysopen (*$$;$) {
     push @{ $files_being_mocked{$abs_path}->{'fhs'} }, $_[0];
     Scalar::Util::weaken( $files_being_mocked{$abs_path}->{'fhs'}[-1] ) if ref $_[0];
 
+    # Register in reverse lookup for O(1) _fh_to_file resolution.
+    $_fh_to_path{"$_[0]"} = $abs_path;
+    if ( ref $_[0] && tied( *{ $_[0] } ) ) {
+        tied( *{ $_[0] } )->{'_fh_string'} = "$_[0]";
+    }
+
     # O_APPEND
     if ( $sysopen_mode & O_APPEND ) {
         seek $_[0], length $mock_file->{'contents'}, 0;
@@ -3352,6 +3364,9 @@ sub __opendir (*$) {
     $mock_dir->{'obj'} = Test::MockFile::DirHandle->new( $abs_path, $mock_dir->contents() );
     $mock_dir->{'fh'}  = "$_[0]";
 
+    # Register in reverse lookup for O(1) _fh_to_file resolution.
+    $_fh_to_path{"$_[0]"} = $abs_path;
+
     return 1;
 
 }
diff --git a/lib/Test/MockFile/FileHandle.pm b/lib/Test/MockFile/FileHandle.pm
index 0a8ce22..88f338e 100644
--- a/lib/Test/MockFile/FileHandle.pm
+++ b/lib/Test/MockFile/FileHandle.pm
@@ -15,9 +15,11 @@ use Scalar::Util ();
 our $VERSION = '0.038';
 
 my $files_being_mocked;
+my $fh_to_path;
 {
     no warnings 'once';
     $files_being_mocked = \%Test::MockFile::files_being_mocked;
+    $fh_to_path         = \%Test::MockFile::_fh_to_path;
 }
 
 =head1 NAME
@@ -481,6 +483,11 @@ sub CLOSE {
         } @{ $mock->{'fhs'} };
     }
 
+    # Remove from reverse fh-to-path lookup.
+    if ( my $fh_str = $self->{'_fh_string'} ) {
+        delete $fh_to_path->{$fh_str};
+    }
+
     return 1;
 }