diff --git a/extension/src/VisualizationBackend/RbVisualizationSupport.ts b/extension/src/VisualizationBackend/RbVisualizationSupport.ts
index 434cede..6aac377 100644
--- a/extension/src/VisualizationBackend/RbVisualizationSupport.ts
+++ b/extension/src/VisualizationBackend/RbVisualizationSupport.ts
@@ -1,4 +1,4 @@
-import { DataExtractionResult, DataResult } from "@hediet/debug-visualizer-data-extraction";
+import { DataExtractionResult, DataExtractorId, DataResult } from "@hediet/debug-visualizer-data-extraction";
 import { hotClass, registerUpdateReconciler } from "@hediet/node-reload";
 import { Config } from "../Config";
 import { DebuggerViewProxy } from "../proxies/DebuggerViewProxy";
@@ -96,10 +96,9 @@ class RbVisualizationBackend extends VisualizationBackendBase {
 					}
 				};
 			}
-			const preferredId = preferredExtractorId || '';
-			const wrappedExpr = `
-				DebugVisualizer.to_debug_visualizer_protocol_json("${preferredId}", ${expression})
-			`;
+
+			const wrappedExpr = await this._getExpression(preferredExtractorId || '', expression, frameId);
+
 			const reply = await this.debugSession.evaluate({
 				expression: wrappedExpr,
 				frameId,
@@ -139,4 +138,21 @@ class RbVisualizationBackend extends VisualizationBackendBase {
 			};
 		}
 	}
+
+	private async _getExpression(preferredId: string | DataExtractorId, expression: string, frameId: number | undefined) {
+		// From version 1.7, `::DEBUGGER__::NaiveString` class is introduced to get whole body of String.
+		// https://github.com/ruby/debug/commit/2f510f0ed685da2f78b370fb8898ffbd2a4f1cf7
+		const reply = await this.debugSession.evaluate({
+			expression: "defined? ::DEBUGGER__::NaiveString",
+			frameId,
+			context: this.defaultContext
+		});
+		const wrappedExpr = `DebugVisualizer.to_debug_visualizer_protocol_json("${preferredId}", ${expression})`;
+		// Because reply.result is '"constant"', we use includes method here.
+		if (reply.result.includes('constant')) {
+			return `::DEBUGGER__::NaiveString.new(${wrappedExpr})`;
+		} else {
+			return wrappedExpr;
+		}
+	}
 }