diff --git a/include/minja/minja.hpp b/include/minja/minja.hpp
index 604e613..dd0ae6c 100644
--- a/include/minja/minja.hpp
+++ b/include/minja/minja.hpp
@@ -1270,6 +1270,11 @@ class BinaryOpExpr : public Expression {
           }
 
           auto r = right->evaluate(context);
+          if (op != Op::Eq && op != Op::Ne) {
+            if (r.is_null() || (l.is_null() && (op != Op::In && op != Op::NotIn))) {
+              throw std::runtime_error("unsupported operand type(s)");
+            }
+          }
           switch (op) {
               case Op::StrConcat: return l.to_str() + r.to_str();
               case Op::Add:       return l + r;
@@ -2147,11 +2152,11 @@ class Parser {
     }
 
     std::runtime_error unexpected(const TemplateToken & token) const {
-      return std::runtime_error("Unexpected " + TemplateToken::typeToString(token.type)
+      return std::runtime_error("Encountered unknown tag '" + TemplateToken::typeToString(token.type) + "'"
         + error_location_suffix(*template_str, token.location.pos));
     }
     std::runtime_error unterminated(const TemplateToken & token) const {
-      return std::runtime_error("Unterminated " + TemplateToken::typeToString(token.type)
+      return std::runtime_error("Unexpected end of template. Jinja was looking for the following tags: '" + TemplateToken::typeToString(token.type) + "'"
         + error_location_suffix(*template_str, token.location.pos));
     }
 
diff --git a/tests/test-syntax.cpp b/tests/test-syntax.cpp
index 54088b8..db1787d 100644
--- a/tests/test-syntax.cpp
+++ b/tests/test-syntax.cpp
@@ -484,28 +484,33 @@ TEST(SyntaxTest, SimpleCases) {
         "",
         render("{% if 1 %}{% elif 1 %}{% else %}{% endif %}", {}, {}));
 
+    EXPECT_THAT([]() { render(R"({{ 'a' + None }})", {}, {}); }, testing::Throws<std::runtime_error>());
+    EXPECT_THAT([]() { render(R"({{ None + 'b' }})", {}, {}); }, testing::Throws<std::runtime_error>());
+    EXPECT_THAT([]() { render(R"({{ 'a' in None }})", {}, {}); }, testing::Throws<std::runtime_error>());
+    EXPECT_EQ(
+        "False,True,False",
+        render(R"({{ None in [] }},{{ None == None }},{{ None != None }})", {}, {}));
 
     if (!getenv("USE_JINJA2")) {
         // TODO: capture stderr from jinja2 and test these.
-
         EXPECT_THAT([]() { render("{%- set _ = [].pop() -%}", {}, {}); }, ThrowsWithSubstr("pop from empty list"));
         EXPECT_THAT([]() { render("{%- set _ = {}.pop() -%}", {}, {}); }, ThrowsWithSubstr("pop"));
         EXPECT_THAT([]() { render("{%- set _ = {}.pop('foooo') -%}", {}, {}); }, ThrowsWithSubstr("foooo"));
 
-        EXPECT_THAT([]() { render("{% else %}", {}, {}); }, ThrowsWithSubstr("Unexpected else"));
+        EXPECT_THAT([]() { render("{% else %}", {}, {}); }, ThrowsWithSubstr("Encountered unknown tag 'else'"));
 
-        EXPECT_THAT([]() { render("{% else %}", {}, {}); }, ThrowsWithSubstr("Unexpected else"));
-        EXPECT_THAT([]() { render("{% endif %}", {}, {}); }, ThrowsWithSubstr("Unexpected endif"));
-        EXPECT_THAT([]() { render("{% elif 1 %}", {}, {}); }, ThrowsWithSubstr("Unexpected elif"));
-        EXPECT_THAT([]() { render("{% endfor %}", {}, {}); }, ThrowsWithSubstr("Unexpected endfor"));
-        EXPECT_THAT([]() { render("{% endfilter %}", {}, {}); }, ThrowsWithSubstr("Unexpected endfilter"));
+        EXPECT_THAT([]() { render("{% else %}", {}, {}); }, ThrowsWithSubstr("Encountered unknown tag 'else'"));
+        EXPECT_THAT([]() { render("{% endif %}", {}, {}); }, ThrowsWithSubstr("Encountered unknown tag 'endif'"));
+        EXPECT_THAT([]() { render("{% elif 1 %}", {}, {}); }, ThrowsWithSubstr("Encountered unknown tag 'elif'"));
+        EXPECT_THAT([]() { render("{% endfor %}", {}, {}); }, ThrowsWithSubstr("Encountered unknown tag 'endfor'"));
+        EXPECT_THAT([]() { render("{% endfilter %}", {}, {}); }, ThrowsWithSubstr("Encountered unknown tag 'endfilter'"));
 
-        EXPECT_THAT([]() { render("{% if 1 %}", {}, {}); }, ThrowsWithSubstr("Unterminated if"));
-        EXPECT_THAT([]() { render("{% for x in 1 %}", {}, {}); }, ThrowsWithSubstr("Unterminated for"));
-        EXPECT_THAT([]() { render("{% generation %}", {}, {}); }, ThrowsWithSubstr("Unterminated generation"));
-        EXPECT_THAT([]() { render("{% if 1 %}{% else %}", {}, {}); }, ThrowsWithSubstr("Unterminated if"));
-        EXPECT_THAT([]() { render("{% if 1 %}{% else %}{% elif 1 %}{% endif %}", {}, {}); }, ThrowsWithSubstr("Unterminated if"));
-        EXPECT_THAT([]() { render("{% filter trim %}", {}, {}); }, ThrowsWithSubstr("Unterminated filter"));
+        EXPECT_THAT([]() { render("{% if 1 %}", {}, {}); }, ThrowsWithSubstr("Unexpected end of template. Jinja was looking for the following tags: 'if'"));
+        EXPECT_THAT([]() { render("{% for x in 1 %}", {}, {}); }, ThrowsWithSubstr("Unexpected end of template. Jinja was looking for the following tags: 'for'"));
+        EXPECT_THAT([]() { render("{% generation %}", {}, {}); }, ThrowsWithSubstr("Unexpected end of template. Jinja was looking for the following tags: 'generation'"));
+        EXPECT_THAT([]() { render("{% if 1 %}{% else %}", {}, {}); }, ThrowsWithSubstr("Unexpected end of template. Jinja was looking for the following tags: 'if'"));
+        EXPECT_THAT([]() { render("{% if 1 %}{% else %}{% elif 1 %}{% endif %}", {}, {}); }, ThrowsWithSubstr("Unexpected end of template. Jinja was looking for the following tags: 'if'"));
+        EXPECT_THAT([]() { render("{% filter trim %}", {}, {}); }, ThrowsWithSubstr("Unexpected end of template. Jinja was looking for the following tags: 'filter'"));
     }
 
     EXPECT_EQ(