diff --git a/reactor-netty-http/src/main/java/reactor/netty/http/server/DefaultHttpForwardedHeaderHandler.java b/reactor-netty-http/src/main/java/reactor/netty/http/server/DefaultHttpForwardedHeaderHandler.java
index b9fdb4afe..259e7a980 100644
--- a/reactor-netty-http/src/main/java/reactor/netty/http/server/DefaultHttpForwardedHeaderHandler.java
+++ b/reactor-netty-http/src/main/java/reactor/netty/http/server/DefaultHttpForwardedHeaderHandler.java
@@ -138,7 +138,11 @@ private static String parseForwardedPrefix(String prefixHeader) {
 			}
 			prefix.append((endIndex != rawPrefix.length() ? rawPrefix.substring(0, endIndex) : rawPrefix));
 		}
-		return prefix.toString();
+		String parsedPrefix = prefix.toString();
+		if (!parsedPrefix.isEmpty() && DEFAULT_FORWARDED_HEADER_VALIDATION && !parsedPrefix.startsWith("/")) {
+			throw new IllegalArgumentException("X-Forwarded-Prefix did not start with a slash (\"/\"): " + prefixHeader);
+		}
+		return parsedPrefix;
 	}
 
 	private static String[] tokenizeToStringArray(String str) {
diff --git a/reactor-netty-http/src/test/java/reactor/netty/http/server/ConnectionInfoTests.java b/reactor-netty-http/src/test/java/reactor/netty/http/server/ConnectionInfoTests.java
index 8de955518..0bc45f72c 100644
--- a/reactor-netty-http/src/test/java/reactor/netty/http/server/ConnectionInfoTests.java
+++ b/reactor-netty-http/src/test/java/reactor/netty/http/server/ConnectionInfoTests.java
@@ -315,14 +315,30 @@ void xForwardedHostPortIncludedAndXForwardedPort(boolean useCustomForwardedHandl
 	void xForwardedPrefix(boolean useCustomForwardedHandler) {
 		testClientRequest(
 				clientRequestHeaders -> {
-					clientRequestHeaders.add("X-Forwarded-Prefix", "test-prefix");
+					clientRequestHeaders.add("X-Forwarded-Prefix", "/test-prefix");
 				},
 				serverRequest -> {
-					Assertions.assertThat(serverRequest.forwardedPrefix()).isEqualTo("test-prefix");
+					Assertions.assertThat(serverRequest.forwardedPrefix()).isEqualTo("/test-prefix");
 				},
 				useCustomForwardedHandler);
 	}
 
+	@Test
+	void xForwardedPrefixWithoutForwardSlash() {
+		testClientRequest(
+				clientRequestHeaders -> {
+					clientRequestHeaders.add("X-Forwarded-Prefix", "forward-slash-missing");
+				},
+				serverRequest -> {
+
+				},
+				null,
+				httpClient -> httpClient,
+				httpServer -> httpServer.port(8080),
+				false,
+				true);
+	}
+
 	@ParameterizedTest
 	@CsvSource(value = {
 			"/first,/second    | /first/second",
@@ -376,7 +392,7 @@ void xForwardedMultipleHeaders(boolean useCustomForwardedHandler) {
 					clientRequestHeaders.add("X-Forwarded-Port", "8081");
 					clientRequestHeaders.add("X-Forwarded-Proto", "http");
 					clientRequestHeaders.add("X-Forwarded-Proto", "https");
-					clientRequestHeaders.add("X-Forwarded-Prefix", "test-prefix");
+					clientRequestHeaders.add("X-Forwarded-Prefix", "/test-prefix");
 				},
 				serverRequest -> {
 					Assertions.assertThat(serverRequest.hostAddress().getHostString()).isEqualTo("192.168.0.1");
@@ -384,7 +400,7 @@ void xForwardedMultipleHeaders(boolean useCustomForwardedHandler) {
 					Assertions.assertThat(serverRequest.hostName()).isEqualTo("192.168.0.1");
 					Assertions.assertThat(serverRequest.hostPort()).isEqualTo(8080);
 					Assertions.assertThat(serverRequest.scheme()).isEqualTo("http");
-					Assertions.assertThat(serverRequest.forwardedPrefix()).isEqualTo("test-prefix");
+					Assertions.assertThat(serverRequest.forwardedPrefix()).isEqualTo("/test-prefix");
 				},
 				useCustomForwardedHandler);
 	}