diff --git a/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandler.java b/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandler.java
index 1478096c4238d..db0e7dd374ba0 100644
--- a/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandler.java
+++ b/independent-projects/resteasy-reactive/server/runtime/src/main/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandler.java
@@ -131,7 +131,9 @@ static final class CapturingInputStream extends InputStream {
         @Override
         public int read() throws IOException {
             int res = delegate.read();
-            baos.write(res);
+            if (res != -1) {
+                baos.write(res);
+            }
             return res;
         }
     }
diff --git a/independent-projects/resteasy-reactive/server/runtime/src/test/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandlerTest.java b/independent-projects/resteasy-reactive/server/runtime/src/test/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandlerTest.java
new file mode 100644
index 0000000000000..420b69a90c8a7
--- /dev/null
+++ b/independent-projects/resteasy-reactive/server/runtime/src/test/java/org/jboss/resteasy/reactive/server/handlers/FormBodyHandlerTest.java
@@ -0,0 +1,19 @@
+package org.jboss.resteasy.reactive.server.handlers;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import org.junit.jupiter.api.Test;
+
+public class FormBodyHandlerTest {
+    @Test
+    public void capturingInputStreamDiscardsNegativeOne() throws IOException {
+        final String string = "this is a string";
+        final ByteArrayInputStream bais = new ByteArrayInputStream(string.getBytes(UTF_8));
+        final FormBodyHandler.CapturingInputStream captured = new FormBodyHandler.CapturingInputStream(bais);
+        assertEquals(string, new String(captured.readAllBytes(), UTF_8));
+        assertEquals(string, captured.baos.toString(UTF_8));
+    }
+}
diff --git a/independent-projects/resteasy-reactive/server/vertx/src/test/java/org/jboss/resteasy/reactive/server/vertx/test/form/FormUrlencodedCorruptionTest.java b/independent-projects/resteasy-reactive/server/vertx/src/test/java/org/jboss/resteasy/reactive/server/vertx/test/form/FormUrlencodedCorruptionTest.java
new file mode 100644
index 0000000000000..ecbad7e5c27ad
--- /dev/null
+++ b/independent-projects/resteasy-reactive/server/vertx/src/test/java/org/jboss/resteasy/reactive/server/vertx/test/form/FormUrlencodedCorruptionTest.java
@@ -0,0 +1,91 @@
+package org.jboss.resteasy.reactive.server.vertx.test.form;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.hamcrest.Matchers.is;
+
+import io.restassured.RestAssured;
+import java.net.URLEncoder;
+import javax.ws.rs.Consumes;
+import javax.ws.rs.POST;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.MultivaluedMap;
+import org.jboss.resteasy.reactive.RestForm;
+import org.jboss.resteasy.reactive.server.vertx.test.framework.ResteasyReactiveUnitTest;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+public class FormUrlencodedCorruptionTest {
+    @RegisterExtension
+    static ResteasyReactiveUnitTest TEST = new ResteasyReactiveUnitTest()
+            .withApplicationRoot(jar -> jar.addClasses(TestResource.class));
+
+    @Test
+    public void testBound() {
+        testWithUri("/test/bound");
+    }
+
+    @Test
+    public void testUnbound() {
+        testWithUri("/test/unbound");
+    }
+
+    @Test
+    public void testMixed() {
+        testWithUri("/test/mixed");
+    }
+
+    private void testWithUri(String uri) {
+        String first = "Gaius Julius Caesar";
+        String next = "Gnaeus Pompeius Magnus";
+        String last = "Marcus Licinius Crassus";
+        String body = encode("first", first, "next", next, "last", last);
+        RestAssured
+                .given()
+                .contentType(MediaType.APPLICATION_FORM_URLENCODED)
+                .body(body)
+                .post(uri)
+                .then()
+                .statusCode(200)
+                .body(is(String.join("\n", first, next, last)));
+    }
+
+    private static String encode(String... args) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < args.length; i += 2) {
+            if (i > 0) {
+                sb.append('&');
+            }
+            sb.append(URLEncoder.encode(args[i], UTF_8)).append('=').append(URLEncoder.encode(args[i + 1], UTF_8));
+        }
+        return sb.toString();
+    }
+
+    @Path("test")
+    public static class TestResource {
+        @Path("bound")
+        @POST
+        @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
+        @Produces(MediaType.TEXT_PLAIN)
+        public String bound(@RestForm String first, @RestForm String next, @RestForm String last) {
+            return String.join("\n", first, next, last);
+        }
+
+        @Path("unbound")
+        @POST
+        @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
+        @Produces(MediaType.TEXT_PLAIN)
+        public String unbound(MultivaluedMap<String, String> params) {
+            return String.join("\n", params.getFirst("first"), params.getFirst("next"), params.getFirst("last"));
+        }
+
+        @Path("mixed")
+        @POST
+        @Consumes(MediaType.APPLICATION_FORM_URLENCODED)
+        @Produces(MediaType.TEXT_PLAIN)
+        public String mixed(@RestForm String first, MultivaluedMap<String, String> params) {
+            return String.join("\n", first, params.getFirst("next"), params.getFirst("last"));
+        }
+    }
+}