Index: src/wp-includes/functions.php
===================================================================
--- src/wp-includes/functions.php	(revision 45905)
+++ src/wp-includes/functions.php	(working copy)
@@ -7296,3 +7296,19 @@
 function is_php_version_compatible( $required ) {
 	return empty( $required ) || version_compare( phpversion(), $required, '>=' );
 }
+
+/**
+ * Check if two numbers are nearly the same.
+ * 
+ * This is similar to using `round()` but the precision is more fine-grained.
+ *
+ * @since 5.3.0
+ * 
+ * @param int|float $expected  The expected value.
+ * @param int|float $actual    The actual number.
+ * @param int|float $precision The allowed variation.
+ * @return bool Whether the numbers match whithin the specified precision.
+ */
+function wp_fuzzy_number_match( $expected, $actual, $precision = 1 ) {
+	return abs( (float) $expected - (float) $actual ) <= $precision;
+}
Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 45905)
+++ src/wp-includes/media.php	(working copy)
@@ -543,8 +543,28 @@
 		return $output;
 	}
 
+	// Stop if the destination size is larger than the original image dimensions.
+	if ( empty( $dest_h ) ) {
+		if ( $orig_w < $dest_w ) {
+			return false;
+		}
+	} elseif ( empty( $dest_w ) ) {
+		if ( $orig_h < $dest_h ) {
+			return false;
+		}
+	} else {
+		if ( $orig_w < $dest_w && $orig_h < $dest_h ) {
+			return false;
+		}
+	}
+
 	if ( $crop ) {
-		// crop the largest possible portion of the original image that we can size to $dest_w x $dest_h
+		// Crop the largest possible portion of the original image that we can size to $dest_w x $dest_h.
+		// Note that the requested crop dimensions are used as a maximum bounding box for the original image.
+		// If the original image's width or height is less than the requested width or height
+		// only the greater one will be cropped.
+		// For example when the original image is 600x300, and the requested crop dimensions are 400x400,
+		// the resulting image will be 400x300.
 		$aspect_ratio = $orig_w / $orig_h;
 		$new_w        = min( $dest_w, $orig_w );
 		$new_h        = min( $dest_h, $orig_h );
@@ -584,7 +604,7 @@
 			$s_y = floor( ( $orig_h - $crop_h ) / 2 );
 		}
 	} else {
-		// don't crop, just resize using $dest_w x $dest_h as a maximum bounding box
+		// Resize using $dest_w x $dest_h as a maximum bounding box.
 		$crop_w = $orig_w;
 		$crop_h = $orig_h;
 
@@ -594,15 +614,29 @@
 		list( $new_w, $new_h ) = wp_constrain_dimensions( $orig_w, $orig_h, $dest_w, $dest_h );
 	}
 
-	// if the resulting image would be the same size or larger we don't want to resize it
-	if ( $new_w >= $orig_w && $new_h >= $orig_h && intval( $dest_w ) !== intval( $orig_w ) && intval( $dest_h ) !== intval( $orig_h ) ) {
-		return false;
+	if ( wp_fuzzy_number_match( $new_w, $orig_w ) && wp_fuzzy_number_match( $new_h, $orig_h ) ) {
+		// The new size has virtually the same dimensions as the original image.
+
+		/**
+		 * Filters whether to proceed with making an image sub-size with identical dimensions
+		 * with the original/source image. Differences of 1px may be due to rounding and are ignored.
+		 *
+		 * @since 5.3.0
+		 * 
+		 * @param bool The filtered value.
+		 * @param int  Original image width.
+		 * @param int  Original image height.
+		 */
+		$proceed = (bool) apply_filters( 'wp_image_resize_identical_dimensions', false, $orig_w, $orig_h );
+
+		if ( ! $proceed ) {
+			return false;
+		}
 	}
 
-	// the return array matches the parameters to imagecopyresampled()
+	// The return array matches the parameters to imagecopyresampled().
 	// int dst_x, int dst_y, int src_x, int src_y, int dst_w, int dst_h, int src_w, int src_h
 	return array( 0, 0, (int) $s_x, (int) $s_y, (int) $new_w, (int) $new_h, (int) $crop_w, (int) $crop_h );
-
 }
 
 /**
@@ -664,7 +698,7 @@
 	}
 
 	// If the image dimensions are within 1px of the expected size, we consider it a match.
-	$matched = ( abs( $constrained_size[0] - $expected_size[0] ) <= 1 && abs( $constrained_size[1] - $expected_size[1] ) <= 1 );
+	$matched = ( wp_fuzzy_number_match( $constrained_size[0], $expected_size[0] ) && wp_fuzzy_number_match( $constrained_size[1], $expected_size[1] ) );
 
 	return $matched;
 }
Index: tests/phpunit/tests/image/dimensions.php
===================================================================
--- tests/phpunit/tests/image/dimensions.php	(revision 45905)
+++ tests/phpunit/tests/image/dimensions.php	(working copy)
@@ -131,6 +131,17 @@
 	function test_640x480() {
 		// crop 640x480 to fit 640x480 (no change)
 		$out = image_resize_dimensions( 640, 480, 640, 480, true );
+		$this->assertFalse( $out );
+
+		// resize 640x480 to fit 640x480 (no change)
+		$out = image_resize_dimensions( 640, 480, 640, 480, false );
+		$this->assertFalse( $out );
+
+		// Test with the filter override.
+		add_filter( 'wp_image_resize_identical_dimensions', '__return_true' );
+
+		// crop 640x480 to fit 640x480 (no change)
+		$out = image_resize_dimensions( 640, 480, 640, 480, true );
 		// dst_x, dst_y, src_x, src_y, dst_w, dst_h, src_w, src_h
 		$this->assertEquals( array( 0, 0, 0, 0, 640, 480, 640, 480 ), $out );
 
@@ -138,6 +149,8 @@
 		$out = image_resize_dimensions( 640, 480, 640, 480, false );
 		// dst_x, dst_y, src_x, src_y, dst_w, dst_h, src_w, src_h
 		$this->assertEquals( array( 0, 0, 0, 0, 640, 480, 640, 480 ), $out );
+
+		remove_filter( 'wp_image_resize_identical_dimensions', '__return_true' );
 	}
 
 	/**