diff --git a/classes/helpers/FrmFieldGridHelper.php b/classes/helpers/FrmFieldGridHelper.php
index 30eb37d6cf..527a7693af 100644
--- a/classes/helpers/FrmFieldGridHelper.php
+++ b/classes/helpers/FrmFieldGridHelper.php
@@ -156,7 +156,20 @@ public function maybe_begin_field_wrapper() {
 	 * @return bool
 	 */
 	private function should_first_close_the_active_field_wrapper() {
-		if ( false === $this->parent_li || $this->section_helper ) {
+		if ( false === $this->parent_li ) {
+			return false;
+		}
+
+		/**
+		 * Fields that sit inside an open section are wrapped by that section's own helper, so the
+		 * row here is not theirs to close. set_field() opens the section helper for the section
+		 * field itself, one step ahead of this check, and section_is_open is not set until
+		 * sync_list_size() runs afterwards. Testing both is what keeps the section field subject to
+		 * the width check below rather than being treated as though it were already inside itself.
+		 *
+		 * @see https://github.com/Strategy11/formidable-pro/issues/3820
+		 */
+		if ( $this->section_helper && $this->section_is_open ) {
 			return false;
 		}
 
@@ -260,7 +273,12 @@ public function force_close_field_wrapper() {
 	 * @return void
 	 */
 	private function close_field_wrapper() {
-		$this->maybe_close_section_helper();
+		// Only an open section has a nested wrapper to close. A section helper that set_field() has
+		// just created belongs to the section about to start, so closing this row must leave it alone.
+		if ( $this->section_is_open ) {
+			$this->maybe_close_section_helper();
+		}
+
 		echo '</ul></li>';
 		$this->parent_li           = false;
 		$this->current_list_size   = 0;
diff --git a/tests/phpunit/fields/test_FrmFieldGridHelper.php.php b/tests/phpunit/fields/test_FrmFieldGridHelper.php
similarity index 94%
rename from tests/phpunit/fields/test_FrmFieldGridHelper.php.php
rename to tests/phpunit/fields/test_FrmFieldGridHelper.php
index 3ac2004d32..d43ecce4f2 100644
--- a/tests/phpunit/fields/test_FrmFieldGridHelper.php.php
+++ b/tests/phpunit/fields/test_FrmFieldGridHelper.php
@@ -427,18 +427,13 @@ public function test_a_section_keeps_its_helper_after_the_row_bookkeeping_runs()
 	}
 
 	/**
-	 * Documents the behaviour reported in https://github.com/Strategy11/formidable-pro/issues/3820.
+	 * Covers https://github.com/Strategy11/formidable-pro/issues/3820.
 	 *
-	 * A section is measured through section_size rather than active_field_size, and
-	 * should_first_close_the_active_field_wrapper() returns early while a section helper
-	 * exists, so the width check never runs for the section itself. The narrow field and the
-	 * full width section end up in one row even though they add up to sixteen columns.
-	 *
-	 * The assertion below records what the helper does today. Closing the row before the section
-	 * is only half the fix: close_field_wrapper() also drops the section helper, which
-	 * test_a_section_keeps_its_helper_after_the_row_bookkeeping_runs covers.
+	 * A four column field followed by a full width section adds up to sixteen columns, so the
+	 * section has to start its own row. The section still has to arrive intact, which is why the
+	 * nested row and the end marker are part of the expected layout rather than a bare '[1][2]'.
 	 */
-	public function test_a_section_currently_joins_a_row_it_cannot_fit_in() {
+	public function test_a_section_starts_a_new_row_when_it_cannot_fit() {
 		$layout = $this->get_grid_layout(
 			array(
 				$this->text_spec( 'frm4' ),
@@ -448,7 +443,7 @@ public function test_a_section_currently_joins_a_row_it_cannot_fit_in() {
 			)
 		);
 
-		$this->assertSame( '[1,2[3]4]', $layout, 'Four columns plus a full width section overflow the row, but the row is not closed first.' );
+		$this->assertSame( '[1][2[3]4]', $layout, 'Four columns plus a full width section overflow the row, so the row closes first.' );
 	}
 
 	/**