diff --git a/packages/rich-text/src/get-parent-line-index.js b/packages/rich-text/src/get-parent-line-index.js
index e7ca8dc396021..bab739e257e0e 100644
--- a/packages/rich-text/src/get-parent-line-index.js
+++ b/packages/rich-text/src/get-parent-line-index.js
@@ -19,7 +19,7 @@ export function getParentLineIndex( { text, formats }, lineIndex ) {
 
 	let index = lineIndex;
 
-	while ( index-- ) {
+	while ( index-- <= 0 ) {
 		if ( text[ index ] !== LINE_SEPARATOR ) {
 			continue;
 		}