diff --git a/src/gpu/ops/DrawCustomMeshOp.cpp b/src/gpu/ops/DrawCustomMeshOp.cpp
index 124a23b7b79c2fa3465ce989e3e1c06b8de70a4d..92962dabcc21d5f131152b2d428808de2b464bdb 100644
--- a/src/gpu/ops/DrawCustomMeshOp.cpp
+++ b/src/gpu/ops/DrawCustomMeshOp.cpp
@@ -779,10 +779,13 @@ GrOp::CombineResult CustomMeshOp::onCombineIfPossible(GrOp* t, SkArenaAlloc*, co
         return CombineResult::kCannotCombine;
     }
 
+    if (fVertexCount > INT32_MAX - that->fVertexCount) {
+        return CombineResult::kCannotCombine;
+    }
     if (SkToBool(fIndexCount) != SkToBool(that->fIndexCount)) {
         return CombineResult::kCannotCombine;
     }
-    if (SkToBool(fIndexCount) && fVertexCount + that->fVertexCount > SkToInt(UINT16_MAX)) {
+    if (SkToBool(fIndexCount) && fVertexCount > UINT16_MAX - that->fVertexCount) {
         return CombineResult::kCannotCombine;
     }