diff -Naur cacao/cacao/src/vm/options.cpp cacao/cacao/src/vm/options.cpp
--- cacao/cacao/src/vm/options.cpp	2014-12-12 21:14:45.000000000 +0000
+++ cacao/cacao/src/vm/options.cpp	2015-12-23 21:01:37.644275263 +0000
@@ -26,6 +26,7 @@
 #include "config.h"
 
 #include <limits.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -60,9 +61,9 @@
 
 bool opt_run = true;
 
-s4   opt_heapmaxsize   = 0;     /* maximum heap size                          */
-s4   opt_heapstartsize = 0;     /* initial heap size                          */
-s4   opt_stacksize     = 0;     /* thread stack size                          */
+size_t opt_heapmaxsize   = 0;   /* maximum heap size                          */
+size_t opt_heapstartsize = 0;   /* initial heap size                          */
+size_t opt_stacksize     = 0;   /* thread stack size                          */
 
 bool opt_verbose = false;
 bool opt_debugcolor = false;	/* use ANSI terminal sequences 		      */
diff -Naur cacao/cacao/src/vm/options.hpp cacao/cacao/src/vm/options.hpp
--- cacao/cacao/src/vm/options.hpp	2014-12-12 21:14:45.000000000 +0000
+++ cacao/cacao/src/vm/options.hpp	2015-12-23 21:01:37.645275246 +0000
@@ -26,6 +26,7 @@
 #ifndef OPTIONS_HPP_
 #define OPTIONS_HPP_ 1
 
+#include <stddef.h>                     // for size_t
 #include <stdint.h>                     // for int64_t
 #include <stdio.h>                      // for FILE
 #include "config.h"                     // for ENABLE_DEBUG_FILTER, etc
@@ -77,9 +78,9 @@
 extern bool opt_jar;
 extern bool opt_run;
 
-extern s4   opt_heapmaxsize;
-extern s4   opt_heapstartsize;
-extern s4   opt_stacksize;
+extern size_t opt_heapmaxsize;
+extern size_t opt_heapstartsize;
+extern size_t opt_stacksize;
 
 extern bool opt_verbose;
 extern bool opt_debugcolor;
diff -Naur cacao/cacao/src/vm/vm.cpp cacao/cacao/src/vm/vm.cpp
--- cacao/cacao/src/vm/vm.cpp	2014-12-12 21:14:45.000000000 +0000
+++ cacao/cacao/src/vm/vm.cpp	2015-12-23 21:01:38.046268504 +0000
@@ -29,9 +29,14 @@
 #include <cerrno>
 #include <cstdlib>
 #include <exception>
+#include <stddef.h>
 #include <stdint.h>
 #include <inttypes.h>
 
+#if defined(__LINUX__)
+#include <unistd.h>
+#endif
+
 #include "md-abi.hpp"
 
 #include "mm/codememory.hpp"
@@ -690,6 +695,19 @@
 	opt_heapstartsize = HEAP_STARTSIZE;
 	opt_stacksize     = STACK_SIZE;
 
+#if defined(__LINUX__)
+	// Calculate 1/4 of the physical memory.
+	size_t qmem = sysconf(_SC_PHYS_PAGES) * sysconf(_SC_PAGESIZE) / 4;
+
+	if (qmem > INT32_MAX) {
+		// Allocate no more than 2GB.
+		opt_heapmaxsize = INT32_MAX;
+	} else if (qmem > HEAP_MAXSIZE) {
+		// Otherwise use this if greater than default (128MB).
+		opt_heapmaxsize = qmem;
+	}
+#endif
+
 	// First of all, parse the -XX options.
 	options_xx(vm_args);
 
@@ -896,18 +914,33 @@
 		case OPT_SS:
 			{
 				char c;
-				int j;
+				size_t j;
 
+				errno = 0;
 				c = opt_arg[strlen(opt_arg) - 1];
+				j = strtoul(opt_arg, NULL, 10);
+
+				if (errno)
+					break; // Invalid.
 
 				if ((c == 'k') || (c == 'K')) {
-					j = atoi(opt_arg) * 1024;
+					if (j > SIZE_MAX / 1024)
+						break; // Overflow.
+					else
+						j *= 1024;
 
 				} else if ((c == 'm') || (c == 'M')) {
-					j = atoi(opt_arg) * 1024 * 1024;
-
-				} else
-					j = atoi(opt_arg);
+					if (j > SIZE_MAX / 1024 / 1024)
+						break; // Overflow.
+					else
+						j *= 1024 * 1024;
+
+				} else if ((c == 'g') || (c == 'G')) {
+					if (j > SIZE_MAX / 1024 / 1024 / 1024)
+						break; // Overflow.
+					else
+						j *= 1024 * 1024 * 1024;
+				}
 
 				if (opt == OPT_MX)
 					opt_heapmaxsize = j;
@@ -1498,9 +1531,9 @@
 void VM::print_run_time_config()
 {
 	puts("Run-time variables:\n");
-	printf("  maximum heap size              : %d\n", opt_heapmaxsize);
-	printf("  initial heap size              : %d\n", opt_heapstartsize);
-	printf("  stack size                     : %d\n", opt_stacksize);
+	printf("  maximum heap size              : %lu\n", opt_heapmaxsize);
+	printf("  initial heap size              : %lu\n", opt_heapstartsize);
+	printf("  stack size                     : %lu\n", opt_stacksize);
 
 #if defined(WITH_JAVA_RUNTIME_LIBRARY_GNU_CLASSPATH)
 	printf("  gnu.classpath.boot.library.path: %s\n", _properties.get("gnu.classpath.boot.library.path"));