diff --git a/src/wp-admin/includes/file.php b/src/wp-admin/includes/file.php
index cd3551bfad..538ec2e1ca 100644
--- a/src/wp-admin/includes/file.php
+++ b/src/wp-admin/includes/file.php
@@ -1199,6 +1199,39 @@ function verify_file_signature( $filename, $signatures, $filename_for_errors = f
 
 	}
 
+	// Verify runtime speed of Sodium_Compat is acceptable.
+	if ( ! extension_loaded( 'sodium' ) && ! ParagonIE_Sodium_Compat::polyfill_is_fast() ) {
+		$sodium_compat_is_fast = false;
+
+		// Allow for an old version of Sodium_Compat being loaded before the bundled WordPress one.
+		if ( method_exists( 'ParagonIE_Sodium_Compat', 'runtime_speed_test' ) ) {
+			// Run `ParagonIE_Sodium_Compat::runtime_speed_test()` in optimized integer mode, as that's what WordPress utilises during signing verifications.
+			$old_fastMult                      = ParagonIE_Sodium_Compat::$fastMult;
+			ParagonIE_Sodium_Compat::$fastMult = true;
+			$sodium_compat_is_fast             = ParagonIE_Sodium_Compat::runtime_speed_test( 100, 10 );
+			ParagonIE_Sodium_Compat::$fastMult = $old_fastMult;
+		}
+
+		// This cannot be performed in a reasonable amount of time
+		// https://github.com/paragonie/sodium_compat#help-sodium_compat-is-slow-how-can-i-make-it-fast
+		if ( ! $sodium_compat_is_fast ) {
+			return new WP_Error(
+				'signature_verification_unsupported',
+				sprintf(
+					/* translators: 1: The filename of the package. */
+					__( 'The authenticity of %1$s could not be verified as signature verification is unavailable on this system.' ),
+					'<span class="code">' . esc_html( $filename_for_errors ) . '</span>'
+				),
+				array(
+					'php'                => phpversion(),
+					'sodium'             => defined( 'SODIUM_LIBRARY_VERSION' ) ? SODIUM_LIBRARY_VERSION : ( defined( 'ParagonIE_Sodium_Compat::VERSION_STRING' ) ? ParagonIE_Sodium_Compat::VERSION_STRING : false ),
+					'polyfill_is_fast'   => false,
+					'max_execution_time' => ini_get( 'max_execution_time' ),
+				)
+			);
+		}
+	}
+
 	if ( ! $signatures ) {
 		return new WP_Error(
 			'signature_verification_no_signature',
diff --git a/tests/phpunit/tests/file.php b/tests/phpunit/tests/file.php
index 25a417e512..d36824e4df 100644
--- a/tests/phpunit/tests/file.php
+++ b/tests/phpunit/tests/file.php
@@ -183,4 +183,63 @@ class Tests_File extends WP_UnitTestCase {
 		);
 	}
 
+	/**
+	 * @ticket 47186
+	 */
+	function test_file_signature_functions_as_expected() {
+		$file = wp_tempnam();
+		file_put_contents( $file, 'WordPress' );
+
+		// The signature of 'WordPress' after SHA384 hashing, for verification against the key within self::filter_trust_plus85Tq_key().
+		$expected_signature = 'PmNv0b1ziwJAsVhjdpjd4+PQZidZWSlBm5b+GbbwE9m9HVKDFhEyvyRTHkRYOLypB8P2YvbW7CoOMZqGh8mEAA==';
+
+		add_filter( 'wp_trusted_keys', array( $this, 'filter_trust_plus85Tq_key' ) );
+
+		// Measure how long the call takes.
+		$timer_start = microtime( 1 );
+		$verify      = verify_file_signature( $file, $expected_signature, 'WordPress' );
+		$timer_end   = microtime( 1 );
+		$time_taken  = ( $timer_end - $timer_start );
+
+		unlink( $file );
+		remove_filter( 'wp_trusted_keys', array( $this, 'filter_trust_plus85Tq_key' ) );
+
+		// verify_file_signature() should intentionally never take more than 10s to run.
+		$this->assertLessThan( 10, $time_taken, 'verify_file_signature() took longer than 10 seconds.' );
+
+		// Check to see if the system parameters prevent signature verifications.
+		if ( is_wp_error( $verify ) && 'signature_verification_unsupported' == $verify->get_error_code() ) {
+			$this->markTestSkipped( 'This system does not support Signature Verification.' );
+		}
+
+		$this->assertNotWPError( $verify );
+		$this->assertTrue( $verify );
+	}
+
+	/**
+	 * @ticket 47186
+	 */
+	function test_file_signature_expected_failure() {
+		$file = wp_tempnam();
+		file_put_contents( $file, 'WordPress' );
+
+		// Test an invalid signature.
+		$expected_signature = base64_encode( str_repeat( 'A', SODIUM_CRYPTO_SIGN_PUBLICKEYBYTES ) );
+		$verify             = verify_file_signature( $file, $expected_signature, 'WordPress' );
+		unlink( $file );
+
+		if ( is_wp_error( $verify ) && 'signature_verification_unsupported' == $verify->get_error_code() ) {
+			$this->markTestSkipped( 'This system does not support Signature Verification.' );
+		}
+
+		$this->assertWPError( $verify );
+		$this->assertEquals( 'signature_verification_failed', $verify->get_error_code() );
+	}
+
+	function filter_trust_plus85Tq_key( $keys ) {
+		// A static once-off key used to verify verify_file_signature() works as expected.
+		$keys[] = '+85TqMhxQVAYVW4BSCVkJQvZH4q7z8I9lePbvngvf7A=';
+
+		return $keys;
+	}
 }