diff --git a/Compiler/script2/cs_parser.cpp b/Compiler/script2/cs_parser.cpp
index 93848c84e1..fa177f9968 100644
--- a/Compiler/script2/cs_parser.cpp
+++ b/Compiler/script2/cs_parser.cpp
@@ -3890,6 +3890,14 @@ void AGS::Parser::ParseExpression(SrcList &src, EvaluationResult &eres)
     size_t const expr_start = src.GetCursor();
     SkipToEndOfExpression(src);
     SrcList expression = SrcList(src, expr_start, src.GetCursor() - expr_start);
+    Symbol potential_ident = src.PeekNext();
+    if (_sym.IsIdentifier(potential_ident) &&
+        !_sym.IsPredefined(potential_ident) &&
+        _sym.kNoSrcLocation == _sym.GetDeclared(potential_ident))
+    {
+        UserError("Identifier '%s' is undeclared", _sym.GetName(potential_ident).c_str());
+    }
+
     if (0u == expression.Length())
         UserError("Expected an expression, found '%s' instead", _sym.GetName(src.GetNext()).c_str());
 
diff --git a/Compiler/test2/cc_parser_test_1.cpp b/Compiler/test2/cc_parser_test_1.cpp
index fcc8322c0e..dea01df3a0 100644
--- a/Compiler/test2/cc_parser_test_1.cpp
+++ b/Compiler/test2/cc_parser_test_1.cpp
@@ -2696,3 +2696,66 @@ TEST_F(Compile1, DynarrayOfArray) {
     int compileResult = cc_compile(inpl, scrip);
     ASSERT_STRNE("Ok", (compileResult >= 0) ? "Ok" : last_seen_cc_error());
 }
+
+TEST_F(Compile1, IdentUnknownMessage1)
+{
+    // When an unknown identifier comes up after an expression,
+    // complain about that with a specific error message.
+
+    char const *inpl = "\
+        int foo ()                          \n\
+        {                                   \n\
+            int i;                          \n\
+            while (i < Holzschuh)           \n\
+            {}                              \n\
+        }                                   \n\
+        ";
+
+    int compile_result = cc_compile(inpl, scrip);
+    std::string msg = last_seen_cc_error();
+    ASSERT_STRNE("Ok", (compile_result >= 0) ? "Ok" : msg.c_str());
+    EXPECT_NE(std::string::npos, msg.find("'Holzschuh'"));
+    EXPECT_NE(std::string::npos, msg.find("undeclared"));
+}
+
+TEST_F(Compile1, IdentUnknownMessage2)
+{
+    // When an unknown identifier comes up when an expression is expected,
+    // complain about that with a specific error message.
+
+    char const *inpl = "\
+        int foo ()                          \n\
+        {                                   \n\
+            int i;                          \n\
+            if (Holzschuh)                  \n\
+            {}                              \n\
+        }                                   \n\
+        ";
+
+    int compile_result = cc_compile(inpl, scrip);
+    std::string msg = last_seen_cc_error();
+    ASSERT_STRNE("Ok", (compile_result >= 0) ? "Ok" : msg.c_str());
+    EXPECT_NE(std::string::npos, msg.find("'Holzschuh'"));
+    EXPECT_NE(std::string::npos, msg.find("undeclared"));
+}
+
+TEST_F(Compile1, ExpressionNotFoundMessage2)
+{
+    // When others come up when an expression is expected,
+    // complain about that
+
+    char const *inpl = "\
+        int foo ()                          \n\
+        {                                   \n\
+            int i;                          \n\
+            if (do)                         \n\
+            {}                              \n\
+        }                                   \n\
+        ";
+
+    int compile_result = cc_compile(inpl, scrip);
+    std::string msg = last_seen_cc_error();
+    ASSERT_STRNE("Ok", (compile_result >= 0) ? "Ok" : msg.c_str());
+    EXPECT_NE(std::string::npos, msg.find("an expression"));
+    EXPECT_NE(std::string::npos, msg.find("'do'"));
+}