diff --git a/Python/asdl.c b/Python/asdl.c
index 72329b9..1105d3a 100644
--- a/Python/asdl.c
+++ b/Python/asdl.c
@@ -5,8 +5,22 @@
 asdl_seq_new(int size, PyArena *arena)
 {
 	asdl_seq *seq = NULL;
-	size_t n = sizeof(asdl_seq) +
-			(size ? (sizeof(void *) * (size - 1)) : 0);
+	size_t n = (size ? (sizeof(void *) * (size - 1)) : 0);
+
+	/* check size is sane */
+	if (size < 0 || size == INT_MIN || 
+		(size && ((size - 1) > (PY_SIZE_MAX / sizeof(void *))))) {
+		PyErr_NoMemory();
+		return NULL;
+	}
+
+	/* check if size can be added safely */
+	if (n > PY_SIZE_MAX - sizeof(asdl_seq)) {
+		PyErr_NoMemory();
+		return NULL;
+	}
+
+	n += sizeof(asdl_seq);
 
 	seq = (asdl_seq *)PyArena_Malloc(arena, n);
 	if (!seq) {
@@ -22,8 +36,22 @@
 asdl_int_seq_new(int size, PyArena *arena)
 {
 	asdl_int_seq *seq = NULL;
-	size_t n = sizeof(asdl_seq) +
-			(size ? (sizeof(int) * (size - 1)) : 0);
+	size_t n = (size ? (sizeof(void *) * (size - 1)) : 0);
+
+	/* check size is sane */
+	if (size < 0 || size == INT_MIN || 
+		(size && ((size - 1) > (PY_SIZE_MAX / sizeof(void *))))) {
+			PyErr_NoMemory();
+			return NULL;
+	}
+
+	/* check if size can be added safely */
+	if (n > PY_SIZE_MAX - sizeof(asdl_seq)) {
+		PyErr_NoMemory();
+		return NULL;
+	}
+
+	n += sizeof(asdl_seq);
 
 	seq = (asdl_int_seq *)PyArena_Malloc(arena, n);
 	if (!seq) {
diff --git a/Python/ast.c b/Python/ast.c
index 2c03ad6..3381260 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -3130,6 +3130,9 @@
 	     	buf = (char *)s;
 		u = NULL;
 	} else {
+		/* check for integer overflow */
+		if (len > PY_SIZE_MAX / 4)
+			return NULL;
 		/* "\XX" may become "\u005c\uHHLL" (12 bytes) */
 		u = PyString_FromStringAndSize((char *)NULL, len * 4);
 		if (u == NULL)
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index f82430c..63f2f78 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -2496,11 +2496,43 @@
 					PyString_AS_STRING(item)[0];
 			} else {
 				/* do we need more space? */
-				Py_ssize_t need = j + reslen + len-i-1;
+				Py_ssize_t need = j;
+
+				/* calculate space requirements while checking for overflow */
+				if (need > PY_SSIZE_T_MAX - reslen) {
+					Py_DECREF(item);
+					goto Fail_1;
+				}
+
+				need += reslen;
+
+				if (need > PY_SSIZE_T_MAX - len) {
+					Py_DECREF(item);
+					goto Fail_1;
+				}
+
+				need += len;
+
+				if (need <= i) {
+					Py_DECREF(item);
+					goto Fail_1;
+				}
+
+				need = need - i - 1;
+
+				assert(need >= 0);
+				assert(outlen >= 0);
+
 				if (need > outlen) {
 					/* overallocate, to avoid reallocations */
-					if (need<2*outlen)
+					if (outlen > PY_SSIZE_T_MAX / 2) {
+						Py_DECREF(item);
+						return NULL;
+					}
+
+					if (need<2*outlen) {
 						need = 2*outlen;
+          }
 					if (_PyString_Resize(&result, need)) {
 						Py_DECREF(item);
 						return NULL;
@@ -2592,11 +2624,31 @@
 			else {
 				/* do we need more space? */
 				Py_ssize_t need = j + reslen + len - i - 1;
+        
+				/* check that didnt overflow */
+				if ((j > PY_SSIZE_T_MAX - reslen) ||
+					((j + reslen) > PY_SSIZE_T_MAX - len) ||
+						((j + reslen + len) < i) ||
+							((j + reslen + len - i) <= 0)) {
+					Py_DECREF(item);
+					return NULL;
+				}
+
+				assert(need >= 0);
+				assert(outlen >= 0);
+				
 				if (need > outlen) {
 					/* overallocate,
 					   to avoid reallocations */
-					if (need < 2 * outlen)
-						need = 2 * outlen;
+					if (need < 2 * outlen) {
+            if (outlen > PY_SSIZE_T_MAX / 2) {
+              Py_DECREF(item);
+              return NULL;
+						} else {
+							need = 2 * outlen;
+				    }
+          }
+
 					if (PyUnicode_Resize(
 						&result, need) < 0) {
 						Py_DECREF(item);
diff --git a/Python/compile.c b/Python/compile.c
index 4dfc42d..f40c325 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -225,6 +225,10 @@
 		return ident; /* Don't mangle if class is just underscores */
 	}
 	plen = strlen(p);
+
+	assert(1 <= PY_SSIZE_T_MAX - nlen);
+	assert(1 + nlen <= PY_SSIZE_T_MAX - plen);
+
 	ident = PyString_FromStringAndSize(NULL, 1 + nlen + plen);
 	if (!ident)
 		return 0;
@@ -620,6 +624,8 @@
 	unsigned int *blocks = (unsigned int *)PyMem_Malloc(len*sizeof(int));
 	int i,j, opcode, blockcnt = 0;
 
+	assert(len <= PY_SIZE_MAX / sizeof(int));
+
 	if (blocks == NULL) {
 		PyErr_NoMemory();
 		return NULL;
@@ -1281,6 +1287,12 @@
 		size_t oldsize, newsize;
 		oldsize = b->b_ialloc * sizeof(struct instr);
 		newsize = oldsize << 1;
+
+		if (oldsize > (PY_SIZE_MAX >> 1)) {
+			PyErr_NoMemory();
+			return -1;
+		}
+
 		if (newsize == 0) {
 			PyErr_NoMemory();
 			return -1;
@@ -4091,6 +4103,10 @@
 	a->a_lnotab = PyString_FromStringAndSize(NULL, DEFAULT_LNOTAB_SIZE);
 	if (!a->a_lnotab)
 		return 0;
+	if (nblocks > PY_SIZE_MAX / sizeof(basicblock *)) {
+		PyErr_NoMemory();
+		return 0;
+	}
 	a->a_postorder = (basicblock **)PyObject_Malloc(
 					    sizeof(basicblock *) * nblocks);
 	if (!a->a_postorder) {
@@ -4199,10 +4215,14 @@
 		nbytes = a->a_lnotab_off + 2 * ncodes;
 		len = PyString_GET_SIZE(a->a_lnotab);
 		if (nbytes >= len) {
-			if (len * 2 < nbytes)
+			if ((len <= INT_MAX / 2) && (len * 2 < nbytes))
 				len = nbytes;
-			else
+			else if (len <= INT_MAX / 2)
 				len *= 2;
+			else {
+				PyErr_NoMemory();
+				return 0;
+			}
 			if (_PyString_Resize(&a->a_lnotab, len) < 0)
 				return 0;
 		}
@@ -4221,10 +4241,14 @@
 		nbytes = a->a_lnotab_off + 2 * ncodes;
 		len = PyString_GET_SIZE(a->a_lnotab);
 		if (nbytes >= len) {
-			if (len * 2 < nbytes)
+			if ((len <= INT_MAX / 2) && len * 2 < nbytes)
 				len = nbytes;
-			else
+			else if (len <= INT_MAX / 2)
 				len *= 2;
+			else {
+				PyErr_NoMemory();
+				return 0;
+			}
 			if (_PyString_Resize(&a->a_lnotab, len) < 0)
 				return 0;
 		}
@@ -4283,6 +4307,8 @@
 	if (i->i_lineno && !assemble_lnotab(a, i))
 		return 0;
 	if (a->a_offset + size >= len) {
+		if (len > PY_SSIZE_T_MAX / 2)
+			return 0;
 		if (_PyString_Resize(&a->a_bytecode, len * 2) < 0)
 		    return 0;
 	}