diff --git a/include/behaviortree_cpp/basic_types.h b/include/behaviortree_cpp/basic_types.h
index b61d49c16..99f62bf6b 100644
--- a/include/behaviortree_cpp/basic_types.h
+++ b/include/behaviortree_cpp/basic_types.h
@@ -443,8 +443,9 @@ template <typename T = AnyTypeAllowed>
   auto sname = static_cast<std::string>(name);
   if(!IsAllowedPortName(sname))
   {
-    throw RuntimeError("The name of a port must not be `name` or `ID` "
-                       "and must start with an alphabetic character. "
+    throw RuntimeError("The name of a port must not be `name` or `ID`, "
+                       "must start with an alphabetic character, "
+                       "and must not contain whitespace. "
                        "Underscore is reserved.");
   }
 
diff --git a/src/basic_types.cpp b/src/basic_types.cpp
index ab5e016bb..c6cfb58b4 100644
--- a/src/basic_types.cpp
+++ b/src/basic_types.cpp
@@ -2,6 +2,8 @@
 #include "behaviortree_cpp/tree_node.h"
 #include "behaviortree_cpp/json_export.h"
 
+#include <algorithm>
+#include <cctype>
 #include <cstdlib>
 #include <cstring>
 #include <clocale>
@@ -443,6 +445,10 @@ bool IsAllowedPortName(StringView str)
   {
     return false;
   }
+  if(std::any_of(str.begin(), str.end(), [](unsigned char c) { return std::isspace(c); }))
+  {
+    return false;
+  }
   return !IsReservedAttribute(str);
 }
 
diff --git a/src/xml_parsing.cpp b/src/xml_parsing.cpp
index cf45c568b..740120c0c 100644
--- a/src/xml_parsing.cpp
+++ b/src/xml_parsing.cpp
@@ -214,6 +214,14 @@ void BT::XMLParser::PImpl::loadSubtreeModel(const XMLElement* xml_root)
           {
             throw RuntimeError("Missing attribute [name] in port (SubTree model)");
           }
+          if(!IsAllowedPortName(name))
+          {
+            throw RuntimeError(StrCat("The port name [", name, "] in SubTree [",
+                                      subtree_id,
+                                      "] is not valid. Port names must start "
+                                      "with an alphabetic character and must "
+                                      "not contain whitespace."));
+          }
           if(auto default_value = port_node->Attribute("default"))
           {
             port.setDefaultValue(default_value);
diff --git a/tests/gtest_ports.cpp b/tests/gtest_ports.cpp
index eaaf9733a..d4b21941a 100644
--- a/tests/gtest_ports.cpp
+++ b/tests/gtest_ports.cpp
@@ -861,3 +861,35 @@ TEST(PortTest, VectorAny)
   ASSERT_NO_THROW(status = tree.tickOnce());
   ASSERT_EQ(status, NodeStatus::FAILURE);
 }
+
+TEST(PortTest, IsAllowedPortNameRejectsWhitespace)
+{
+  EXPECT_FALSE(IsAllowedPortName("my port"));
+  EXPECT_FALSE(IsAllowedPortName("port\tname"));
+  EXPECT_FALSE(IsAllowedPortName(" leading"));
+  EXPECT_FALSE(IsAllowedPortName("trailing "));
+  EXPECT_FALSE(IsAllowedPortName("has\nnewline"));
+
+  // Sanity check: valid names still work.
+  EXPECT_TRUE(IsAllowedPortName("valid_port"));
+  EXPECT_TRUE(IsAllowedPortName("anotherPort123"));
+}
+
+TEST(PortTest, WhitespacePortNameInSubtreeModelThrows)
+{
+  BT::BehaviorTreeFactory factory;
+
+  const std::string xml_txt = R"(
+  <root BTCPP_format="4">
+    <BehaviorTree ID="MainTree">
+      <SubTree ID="MySub" my_port="hello" />
+    </BehaviorTree>
+    <TreeNodesModel>
+      <SubTree ID="MySub">
+        <input_port name="my port" />
+      </SubTree>
+    </TreeNodesModel>
+  </root>)";
+
+  EXPECT_THROW(factory.createTreeFromText(xml_txt), BT::RuntimeError);
+}