diff --git a/compiler/cpp/src/parse/t_const_value.h b/compiler/cpp/src/parse/t_const_value.h
index ee658f0..4d5845f 100644
--- a/compiler/cpp/src/parse/t_const_value.h
+++ b/compiler/cpp/src/parse/t_const_value.h
@@ -8,6 +8,7 @@
 #define T_CONST_VALUE_H
 
 #include "t_const.h"
+#include <stdint.h>
 #include <map>
 #include <vector>
 
@@ -30,7 +31,7 @@
 
   t_const_value() {}
 
-  t_const_value(int val) {
+  t_const_value(int64_t val) {
     set_integer(val);
   }
 
@@ -47,12 +48,12 @@
     return stringVal_;
   }
 
-  void set_integer(int val) {
+  void set_integer(int64_t val) {
     valType_ = CV_INTEGER;
     intVal_ = val;
   }
 
-  int get_integer() const {
+  int64_t get_integer() const {
     return intVal_;
   }
 
@@ -97,7 +98,7 @@
   std::map<t_const_value*, t_const_value*> mapVal_;
   std::vector<t_const_value*> listVal_;
   std::string stringVal_;
-  int intVal_;
+  int64_t intVal_;
   double doubleVal_;
 
   t_const_value_type valType_;
diff --git a/compiler/cpp/src/thriftl.ll b/compiler/cpp/src/thriftl.ll
index 21a0dd7..62cdb16 100644
--- a/compiler/cpp/src/thriftl.ll
+++ b/compiler/cpp/src/thriftl.ll
@@ -15,6 +15,8 @@
 
 %{
 
+#include <errno.h>
+
 #include "main.h"
 #include "globals.h"
 #include "parse/t_program.h"
@@ -30,6 +32,11 @@
   exit(1);
 }
 
+void integer_overflow(char* text) {
+  yyerror("This integer is too big: \"%s\"\n", text);
+  exit(1);
+}
+
 %}
 
 /**
@@ -181,12 +188,20 @@
 "yield"              { thrift_reserved_keyword(yytext); }
 
 {intconstant} {
-  yylval.iconst = atoi(yytext);
+  errno = 0;
+  yylval.iconst = strtoll(yytext, NULL, 10);
+  if (errno == ERANGE) {
+    integer_overflow(yytext);
+  }
   return tok_int_constant;
 }
 
 {hexconstant} {
-  sscanf(yytext+2, "%x", &yylval.iconst);
+  errno = 0;
+  yylval.iconst = strtoll(yytext+2, NULL, 16);
+  if (errno == ERANGE) {
+    integer_overflow(yytext);
+  }
   return tok_int_constant;
 }
 
diff --git a/compiler/cpp/src/thrifty.yy b/compiler/cpp/src/thrifty.yy
index 654c85a..f4ff6ef 100644
--- a/compiler/cpp/src/thrifty.yy
+++ b/compiler/cpp/src/thrifty.yy
@@ -13,7 +13,10 @@
  * @author Mark Slee <mcslee@facebook.com>
  */
 
+#define __STDC_LIMIT_MACROS
+#define __STDC_FORMAT_MACROS
 #include <stdio.h>
+#include <inttypes.h>
 #include "main.h"
 #include "globals.h"
 #include "parse/t_program.h"
@@ -35,7 +38,7 @@
  */
 %union {
   char*          id;
-  int            iconst;
+  int64_t        iconst;
   double         dconst;
   bool           tbool;
   t_doc*         tdoc;
@@ -496,6 +499,9 @@
       if ($4 < 0) {
         pwarning(1, "Negative value supplied for enum %s.\n", $2);
       }
+      if ($4 > INT_MAX) {
+        pwarning(1, "64-bit value supplied for enum %s.\n", $2);
+      }
       $$ = new t_enum_value($2, $4);
       if ($1 != NULL) {
         $$->set_doc($1);
@@ -569,6 +575,9 @@
       pdebug("ConstValue => tok_int_constant");
       $$ = new t_const_value();
       $$->set_integer($1);
+      if ($1 < INT32_MIN || $1 > INT32_MAX) {
+        pwarning(1, "64-bit constant \"%"PRIi64"\" may not work in all languages.\n", $1);
+      }
     }
 | tok_dub_constant
     {
diff --git a/test/BrokenConstants.thrift b/test/BrokenConstants.thrift
new file mode 100644
index 0000000..4c47b33
--- /dev/null
+++ b/test/BrokenConstants.thrift
@@ -0,0 +1,6 @@
+const i64 myint = 68719476736
+const i64 broken = 9876543210987654321  // A little over 2^63
+
+enum foo {
+  bar = 68719476736
+}