Changed to Conduitry's suggestion

src/compiler/compile/nodes/Text.ts

@@ -12,7 +12,7 @@ export default class Text extends Node {
 		super(component, parent, scope, info);
 		this.data = info.data;
 
-		if (!component.component_options.preserveWhitespace) {
+		if (!component.component_options.preserveWhitespace && !/[\S\u00A0]/.test(info.data)) {
 			let node = parent;
 			while (node) {
 				if (node.type === 'Element' && node.name === 'pre') {
@@ -21,7 +21,7 @@ export default class Text extends Node {
 				node = node.parent;
 			}
 
-	
+			this.use_space = true;
 		}
 	}
 }

src/compiler/compile/render-dom/wrappers/Text.ts

@@ -54,7 +54,7 @@ export default class TextWrapper extends Wrapper {
 
 		block.add_element(
 			this.var,
-			`@text(${stringify(this.data)})`,
+			this.node.use_space ? `@space()` : `@text(${stringify(this.data)})`,
 			parent_nodes && `@claim_text(${parent_nodes}, ${stringify(this.data)})`,
 			parent_node
 		);

src/runtime/internal/dom.ts

@@ -62,6 +62,9 @@ export function text(data: string) {
 	return document.createTextNode(data);
 }
 
+export function space() {
+	return text(' ');
+}
 
 export function empty() {
 	return text('');