diff --git a/src/match_basic_types.cpp b/src/match_basic_types.cpp
index 4808a18..600a4c7 100644
--- a/src/match_basic_types.cpp
+++ b/src/match_basic_types.cpp
@@ -289,10 +289,10 @@ void MemoryRegion::swap(MemoryRegion& other) {
 }
 void MemoryRegion::grow(std::size_t n) {
 	if (n > size()) {
-		std::size_t nc = std::max(n, (size() * 3) >> 1);
+		std::size_t nc = std::max(n, (size() * 3 + 1) >> 1);
 		void* t = std::realloc(beg_, nc);
 		POTASSCO_CHECK(t, ENOMEM);
-		beg_ = t; end_ = static_cast<unsigned char*>(t)+n;
+		beg_ = t; end_ = static_cast<unsigned char*>(t)+nc;
 	}
 }
 
diff --git a/tests/test_aspif.cpp b/tests/test_aspif.cpp
index 00762f8..0e86797 100644
--- a/tests/test_aspif.cpp
+++ b/tests/test_aspif.cpp
@@ -122,6 +122,35 @@ static int compareRead(std::stringstream& input, ReadObserver& observer, const R
 	}
 	return subset.second;
 }
+TEST_CASE("Test MemoryRegion", "[rule]") {
+	SECTION("starts empty") {
+		MemoryRegion r;
+		REQUIRE(r.size() == 0);
+		REQUIRE(r.begin() == r.end());
+	}
+	SECTION("supports initial size") {
+		MemoryRegion r(256);
+		REQUIRE(r.size() == 256);
+		REQUIRE(std::distance((char*) r.begin(), (char*) r.end()) == 256);
+	}
+	SECTION("grows geometrically") {
+		MemoryRegion r;
+		for (int i = 0; i != 10; ++i) { r.grow(r.size() + 1); }
+		REQUIRE(r.size() >= 50);
+	}
+	SECTION("copies data on grow") {
+		MemoryRegion r;
+		r.grow(12);
+		std::memset(r[0], 'A', 12);
+		r.grow(24);
+		std::memset(r[12], 'B', 12);
+		std::string exp(12, 'A');
+		exp.append(12, 'B');
+		r.grow(r.size() + 1);
+		*(char*) r[24] = 0;
+		REQUIRE(exp == (char*) r.begin());
+	}
+}
 TEST_CASE("Test RuleBuilder", "[rule]") {
 	RuleBuilder rb;
 	SECTION("simple rule") {