diff --git a/graphx/src/main/scala/org/apache/spark/graphx/lib/SVDPlusPlus.scala b/graphx/src/main/scala/org/apache/spark/graphx/lib/SVDPlusPlus.scala
index 7b282ec6d24ee..beb15b0ccbc56 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/lib/SVDPlusPlus.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/lib/SVDPlusPlus.scala
@@ -38,6 +38,17 @@ object SVDPlusPlus {
       var gamma7: Double)
     extends Serializable
 
+  /** Sums two Phase 2 training messages component-wise: both vectors and the scalar. */
+  private[graphx] def combineTrainMessages(
+      g1: (Array[Double], Array[Double], Double),
+      g2: (Array[Double], Array[Double], Double)): (Array[Double], Array[Double], Double) = {
+    val out1 = g1._1.clone()
+    BLAS.nativeBLAS.daxpy(out1.length, 1.0, g2._1, 1, out1, 1)
+    val out2 = g1._2.clone()
+    BLAS.nativeBLAS.daxpy(out2.length, 1.0, g2._2, 1, out2, 1)
+    (out1, out2, g1._3 + g2._3)
+  }
+
   // scalastyle:off line.size.limit
   /**
    * Implement SVD++ based on "Factorization Meets the Neighborhood: a Multifaceted
@@ -152,14 +163,7 @@ object SVDPlusPlus {
       g.cache()
       val t2 = g.aggregateMessages(
         sendMsgTrainF(conf, u),
-        (g1: (Array[Double], Array[Double], Double), g2: (Array[Double], Array[Double], Double)) =>
-        {
-          val out1 = g1._1.clone()
-          BLAS.nativeBLAS.daxpy(out1.length, 1.0, g2._1, 1, out1, 1)
-          val out2 = g1._2.clone()
-          BLAS.nativeBLAS.daxpy(out2.length, 1.0, g2._2, 1, out2, 1)
-          (out1, out2, g1._3 + g2._3)
-        })
+        combineTrainMessages)
       val gJoinT2 = g.outerJoinVertices(t2) {
         (vid: VertexId,
          vd: (Array[Double], Array[Double], Double, Double),
diff --git a/graphx/src/test/scala/org/apache/spark/graphx/lib/SVDPlusPlusSuite.scala b/graphx/src/test/scala/org/apache/spark/graphx/lib/SVDPlusPlusSuite.scala
index da139cec5c3d5..62f257d2cce3c 100644
--- a/graphx/src/test/scala/org/apache/spark/graphx/lib/SVDPlusPlusSuite.scala
+++ b/graphx/src/test/scala/org/apache/spark/graphx/lib/SVDPlusPlusSuite.scala
@@ -49,4 +49,19 @@ class SVDPlusPlusSuite extends SparkFunSuite with LocalSparkContext {
       assert(graph.edges.count() == 0)
     }
   }
+
+  test("SPARK-58177: training-phase message combiner sums both vectors element-wise") {
+    val g1 = (Array(1.0, 2.0), Array(10.0, 20.0), 100.0)
+    val g2 = (Array(3.0, 4.0), Array(30.0, 40.0), 200.0)
+    val (out1, out2, out3) = SVDPlusPlus.combineTrainMessages(g1, g2)
+    // Each component is the element-wise sum of the two messages.
+    assert(out1.toSeq === Seq(4.0, 6.0))
+    assert(out2.toSeq === Seq(40.0, 60.0))
+    assert(out3 === 300.0)
+    // Inputs are cloned, not mutated.
+    assert(g1._1.toSeq === Seq(1.0, 2.0))
+    assert(g1._2.toSeq === Seq(10.0, 20.0))
+    assert(g2._1.toSeq === Seq(3.0, 4.0))
+    assert(g2._2.toSeq === Seq(30.0, 40.0))
+  }
 }