diff --git a/spec/propane_spec.rb b/spec/propane_spec.rb
index 16fff6c..7d0d612 100644
--- a/spec/propane_spec.rb
+++ b/spec/propane_spec.rb
@@ -29,7 +29,7 @@ describe Propane do
     end
     case options[:language]
     when "c"
-      result = system(*%w[gcc -Wall -o spec/run/testparser -Ispec -Ispec/run], *parsers, *test_files)
+      result = system(*%w[gcc -Wall -o spec/run/testparser -Ispec -Ispec/run], *parsers, *test_files, "spec/testutils.c", "-lm")
     when "d"
       result = system(*%w[ldc2 --unittest -of spec/run/testparser -Ispec], *parsers, *test_files, "spec/testutils.d")
     end
@@ -156,7 +156,61 @@ EOF
       end
 
       it "generates a parser that does basic math - user guide example" do
-        write_grammar <<EOF
+        case language
+        when "c"
+          write_grammar <<EOF
+<<
+#include <math.h>
+>>
+
+ptype size_t;
+
+token plus /\\+/;
+token times /\\*/;
+token power /\\*\\*/;
+token integer /\\d+/ <<
+  size_t v = 0u;
+  for (size_t i = 0u; i < match_length; i++)
+  {
+    v *= 10;
+    v += (match[i] - '0');
+  }
+  $$ = v;
+>>
+token lparen /\\(/;
+token rparen /\\)/;
+drop /\\s+/;
+
+Start -> E1 <<
+  $$ = $1;
+>>
+E1 -> E2 <<
+  $$ = $1;
+>>
+E1 -> E1 plus E2 <<
+  $$ = $1 + $3;
+>>
+E2 -> E3 <<
+  $$ = $1;
+>>
+E2 -> E2 times E3 <<
+  $$ = $1 * $3;
+>>
+E3 -> E4 <<
+  $$ = $1;
+>>
+E3 -> E3 power E4 <<
+  $$ = (size_t)pow($1, $3);
+>>
+E4 -> integer <<
+  $$ = $1;
+>>
+E4 -> lparen E1 rparen <<
+  $$ = $2;
+>>
+EOF
+        when "d"
+          write_grammar <<EOF
 <<
 import std.math;
 >>
@@ -207,6 +261,7 @@ E4 -> lparen E1 rparen <<
   $$ = $2;
 >>
 EOF
+        end
         build_parser(language: language)
         compile("spec/test_basic_math_grammar.#{language}", language: language)
         results = run
diff --git a/spec/test_basic_math_grammar.c b/spec/test_basic_math_grammar.c
new file mode 100644
index 0000000..4fa1ce2
--- /dev/null
+++ b/spec/test_basic_math_grammar.c
@@ -0,0 +1,29 @@
+#include "testparser.h"
+#include "testutils.h"
+#include <string.h>
+
+int main()
+{
+    char const * input = "1 + 2 * 3 + 4";
+    p_context_t context;
+    p_context_init(&context, (uint8_t const *)input, strlen(input));
+    assert_eq(P_SUCCESS, p_parse(&context));
+    assert_eq(11, p_result(&context));
+
+    input = "1 * 2 ** 4 * 3";
+    p_context_init(&context, (uint8_t const *)input, strlen(input));
+    assert_eq(P_SUCCESS, p_parse(&context));
+    assert_eq(48, p_result(&context));
+
+    input = "(1 + 2) * 3 + 4";
+    p_context_init(&context, (uint8_t const *)input, strlen(input));
+    assert_eq(P_SUCCESS, p_parse(&context));
+    assert_eq(13, p_result(&context));
+
+    input = "(2 * 2) ** 3 + 4 + 5";
+    p_context_init(&context, (uint8_t const *)input, strlen(input));
+    assert_eq(P_SUCCESS, p_parse(&context));
+    assert_eq(73, p_result(&context));
+
+    return 0;
+}
diff --git a/spec/testutils.c b/spec/testutils.c
new file mode 100644
index 0000000..7180c66
--- /dev/null
+++ b/spec/testutils.c
@@ -0,0 +1,12 @@
+#include <stdio.h>
+#include <assert.h>
+#include <stdbool.h>
+
+void assert_eq_size_t_i(size_t expected, size_t actual, char const * file, size_t line)
+{
+    if (expected != actual)
+    {
+        fprintf(stderr, "%s:%lu: expected %lu, got %lu\n", file, line, expected, actual);
+        assert(false);
+    }
+}
diff --git a/spec/testutils.h b/spec/testutils.h
new file mode 100644
index 0000000..de6ac90
--- /dev/null
+++ b/spec/testutils.h
@@ -0,0 +1,7 @@
+#pragma once
+
+void assert_eq_size_t_i(size_t expected, size_t actual, char const * file, size_t line);
+
+#define assert_eq(expected, actual) \
+    assert_eq_size_t_i(expected, actual, __FILE__, __LINE__)
+