diff --git a/make-3.82-gbuild/function.c b/make-3.82-gbuild/function.c
index e2f6c8c..ff0527f 100644
--- a/make-3.82/function.c
+++ b/make-3.82/function.c
@@ -2333,8 +2333,10 @@ func_call (char *o, char **argv, const char *funcname UNUSED)
   v = lookup_variable (fname, flen);
 
   if (v == 0)
-    warn_undefined (fname, flen);
-
+    {
+      warn_undefined (fname, flen);
+      warn_undefined_function (fname, flen);
+    }
   if (v == 0 || *v->value == '\0')
     return o;
 
diff --git a/make-3.82-gbuild/main.c b/make-3.82-gbuild/main.c
index c6989e3..2f545a7 100644
--- a/make-3.82/main.c
+++ b/make-3.82/main.c
@@ -275,6 +275,11 @@ static int print_usage_flag = 0;
 
 int warn_undefined_variables_flag;
 
+/* If nonzero, we should print a warning message
+   for each attemtp to call an undefined user function.  */
+
+int warn_undefined_functions_flag;
+
 /* If nonzero, always build all targets, regardless of whether
    they appear out of date or not.  */
 
@@ -368,6 +373,8 @@ static const char *const usage[] =
                               Consider FILE to be infinitely new.\n"),
     N_("\
   --warn-undefined-variables  Warn when an undefined variable is referenced.\n"),
+    N_("\
+  --warn-undefined-functions  Warn when an undefined user function is called.\n"),
     NULL
   };
 
@@ -424,6 +431,8 @@ static const struct command_switch switches[] =
     { CHAR_MAX+5, flag, &warn_undefined_variables_flag, 1, 1, 0, 0, 0,
       "warn-undefined-variables" },
     { CHAR_MAX+6, string, &eval_strings, 1, 0, 0, 0, 0, "eval" },
+    { CHAR_MAX+7, flag, &warn_undefined_functions_flag, 1, 1, 0, 0, 0,
+      "warn-undefined-functions" },
     { 0, 0, 0, 0, 0, 0, 0, 0, 0 }
   };
 
diff --git a/make-3.82-gbuild/make.h b/make-3.82-gbuild/make.h
index 60ade4c..f2ebb56 100644
--- a/make-3.82/make.h
+++ b/make-3.82/make.h
@@ -513,7 +513,7 @@ extern int env_overrides, no_builtin_rules_flag, no_builtin_variables_flag;
 extern int print_version_flag, print_directory_flag, check_symlink_flag;
 extern int warn_undefined_variables_flag, posix_pedantic, not_parallel;
 extern int second_expansion, clock_skew_detected, rebuilding_makefiles;
-extern int one_shell;
+extern int one_shell, warn_undefined_functions_flag;
 
 /* can we run commands via 'sh -c xxx' or must we use batch files? */
 extern int batch_mode_shell;
diff --git a/make-3.82-gbuild/variable.h b/make-3.82-gbuild/variable.h
index c215867..02713c1 100644
--- a/make-3.82/variable.h
+++ b/make-3.82/variable.h
@@ -220,6 +220,13 @@ void undefine_variable_in_set (const char *name, unsigned int length,
                                 (int)(l), (n)); \
                               }while(0)
 
+#define warn_undefined_function(n,l) do{\
+                              if (warn_undefined_functions_flag) \
+                                error (reading_file, \
+                                       _("warning: undefined function `%.*s'"), \
+                                (int)(l), (n)); \
+                              }while(0)
+
 char **target_environment (struct file *file);
 
 struct pattern_var *create_pattern_var (const char *target,
--
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