diff --git a/syscall_filter_unittest.cpp b/syscall_filter_unittest.cpp
index 2445f0a..c94aa24 100644
--- a/syscall_filter_unittest.cpp
+++ b/syscall_filter_unittest.cpp
@@ -20,12 +20,76 @@
 #include <fcntl.h> /* For O_WRONLY. */
 
 #include <gtest/gtest.h>
+#include <string>
 
 #include "bpf.h"
 #include "syscall_filter.h"
 #include "syscall_filter_unittest_macros.h"
 #include "util.h"
 
+TEST(util, parse_constant_unsigned) {
+  char *end;
+  long int c = 0;
+  std::string constant;
+
+#if defined(BITS32)
+  constant = "0x80000000";
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  EXPECT_EQ(0x80000000U, static_cast<unsigned long int>(c));
+
+#elif defined(BITS64)
+  constant = "0x8000000000000000";
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  EXPECT_EQ(0x8000000000000000UL, static_cast<unsigned long int>(c));
+#endif
+}
+
+TEST(util, parse_constant_unsigned_toobig) {
+  char *end;
+  long int c = 0;
+  std::string constant;
+
+#if defined(BITS32)
+  constant = "0x100000000";  // Too big for 32-bit unsigned long int.
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  // Error case should return 0.
+  EXPECT_EQ(0, c);
+
+#elif defined(BITS64)
+  constant = "0x10000000000000000";
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  // Error case should return 0.
+  EXPECT_EQ(0, c);
+#endif
+}
+
+TEST(util, parse_constant_signed) {
+  char *end;
+  long int c = 0;
+  std::string constant = "-1";
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  EXPECT_EQ(-1, c);
+}
+
+TEST(util, parse_constant_signed_toonegative) {
+  char *end;
+  long int c = 0;
+  std::string constant;
+
+#if defined(BITS32)
+  constant = "-0x80000001";
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  // Error case should return 0.
+  EXPECT_EQ(0, c);
+
+#elif defined(BITS64)
+  constant = "-0x8000000000000001";
+  c = parse_constant(const_cast<char*>(constant.c_str()), &end);
+  // Error case should return 0.
+  EXPECT_EQ(0, c);
+#endif
+}
+
 /* Test that setting one BPF instruction works. */
 TEST(bpf, set_bpf_instr) {
   struct sock_filter instr;