diff --git a/src/rcheevos/memref.c b/src/rcheevos/memref.c
index 380ae0cf..038ea935 100644
--- a/src/rcheevos/memref.c
+++ b/src/rcheevos/memref.c
@@ -107,7 +107,12 @@ int rc_parse_memref(const char** memaddr, uint8_t* size, uint32_t* address) {
       /* case 'y': case 'Y': 64 bit? */
       /* case 'z': case 'Z': 128 bit? */
 
-      case '0': case '1': case '2': case '3': case '4':
+      case '0':
+        if (*aux == 'x') /* user mistyped an extra 0x: 0x0xabcd */
+          return RC_INVALID_MEMORY_OPERAND;
+        /* fallthrough */
+
+      case '1': case '2': case '3': case '4':
       case '5': case '6': case '7': case '8': case '9':
       case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
       case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
diff --git a/test/rcheevos/test_operand.c b/test/rcheevos/test_operand.c
index 60bd1d9e..ed12fe04 100644
--- a/test/rcheevos/test_operand.c
+++ b/test/rcheevos/test_operand.c
@@ -187,6 +187,9 @@ static void test_parse_memory_references() {
   TEST_PARAMS4(test_parse_operand, "0xHABCD", RC_OPERAND_ADDRESS, RC_MEMSIZE_8_BITS, 0xABCDU);
   TEST_PARAMS4(test_parse_operand, "0xhabcd", RC_OPERAND_ADDRESS, RC_MEMSIZE_8_BITS, 0xABCDU);
   TEST_PARAMS4(test_parse_operand, "fFABCD", RC_OPERAND_ADDRESS, RC_MEMSIZE_FLOAT, 0xABCDU);
+
+  /* doubled up prefix */
+  TEST_PARAMS3(test_parse_error_operand, "0x0xH1234", 0, RC_INVALID_MEMORY_OPERAND);
 }
 
 static void test_parse_delta_memory_references() {
diff --git a/test/rcheevos/test_richpresence.c b/test/rcheevos/test_richpresence.c
index 82d05648..d6388284 100644
--- a/test/rcheevos/test_richpresence.c
+++ b/test/rcheevos/test_richpresence.c
@@ -390,6 +390,12 @@ static void test_conditional_display_unnecessary_measured_indirect() {
   assert_richpresence_output(richpresence, &memory, "True");
 }
 
+static void test_conditional_display_invalid() {
+  int lines_read = 0;
+  ASSERT_NUM_EQUALS(rc_richpresence_size_lines("Display:\n?I:0x0x0000=1?True\nFalse\n", &lines_read), RC_INVALID_MEMORY_OPERAND);
+  ASSERT_NUM_EQUALS(lines_read, 2);
+}
+
 static void test_macro_value_adjusted_negative() {
   uint8_t ram[] = { 0x00, 0x12, 0x34, 0xAB, 0x56 };
   memory_t memory;
@@ -526,6 +532,10 @@ static void test_macro_value_remember_recall() {
   assert_richpresence_output(richpresence, &memory, "Result is 3");
 }
 
+static void test_macro_value_invalid() {
+  ASSERT_NUM_EQUALS(rc_richpresence_size("Format:Points\nFormatType=VALUE\n\nDisplay:\n@Points(0x0x0001) Points"), RC_INVALID_MEMORY_OPERAND);
+}
+
 static void test_macro_hundreds() {
   uint8_t ram[] = { 0x00, 0x12, 0x34, 0xAB, 0x56 };
   memory_t memory;
@@ -1342,6 +1352,7 @@ void test_richpresence(void) {
   TEST(test_conditional_display_indirect);
   TEST(test_conditional_display_unnecessary_measured);
   TEST(test_conditional_display_unnecessary_measured_indirect);
+  TEST(test_conditional_display_invalid);
 
   /* value macros */
   TEST(test_macro_value);
@@ -1355,6 +1366,7 @@ void test_richpresence(void) {
   TEST(test_macro_value_divide_by_zero);
   TEST(test_macro_value_divide_by_self);
   TEST(test_macro_value_remember_recall);
+  TEST(test_macro_value_invalid);
 
   /* hundreds macro */
   TEST(test_macro_hundreds);