diff --git a/src/assembler/parse_util.c b/src/assembler/parse_util.c
index cf256cd..855e9ac 100644
--- a/src/assembler/parse_util.c
+++ b/src/assembler/parse_util.c
@@ -8,12 +8,57 @@
 #include "directives.h"
 
 /*
-    Read in an integer starting at str and ending the character before end.
+    Read in a boolean argument from the given line and store it in *result.
 
-    Store the value in *result and return true on success; else return false.
+    auto_val is used if the argument's value is "auto". Return true on success
+    and false on failure; in the latter case, *result is not modified.
 */
-static inline bool read_integer(uint32_t *result, const char *str, const char *end)
+bool parse_bool(bool *result, const ASMLine *line, const char *directive, bool auto_val)
+{
+    const char *arg = line->data + (DIRECTIVE_OFFSET(line, directive) + 1);
+    ssize_t len = line->length - (DIRECTIVE_OFFSET(line, directive) + 1);
+
+    if (len <= 0 || len > 5)
+        return false;
+
+    switch (len) {
+        case 1:  // 0, 1
+            if (*arg == '0' || *arg == '1')
+                return (*result = *arg - '0'), true;
+            return false;
+        case 2:  // on
+            if (!strncmp(arg, "on", 2))
+                return (*result = true), true;
+            return false;
+        case 3:  // off
+            if (!strncmp(arg, "off", 3))
+                return (*result = false), true;
+            return false;
+        case 4:  // true, auto
+            if (!strncmp(arg, "true", 4))
+                return (*result = true), true;
+            if (!strncmp(arg, "auto", 4))
+                return (*result = auto_val), true;
+            return false;
+        case 5:  // false
+            if (!strncmp(arg, "false", 5))
+                return (*result = false), true;
+            return false;
+    }
+    return false;
+}
+
+/*
+    Read in a 32-bit int argument from the given line and store it in *result.
+
+    Return true on success and false on failure; in the latter case, *result is
+    not modified.
+*/
+bool parse_uint32(uint32_t *result, const ASMLine *line, const char *directive)
 {
+    const char *str = line->data + (DIRECTIVE_OFFSET(line, directive) + 1);
+    const char *end = str + (line->length - (DIRECTIVE_OFFSET(line, directive) + 1));
+
     if (end - str <= 0)
         return false;
 
@@ -30,7 +75,7 @@ static inline bool read_integer(uint32_t *result, const char *str, const char *e
                 value = (value * 0x10) + 0xA + (*str - 'a');
             else
                 return false;
-            if (value >= UINT32_MAX)
+            if (value > UINT32_MAX)
                 return false;
             str++;
         }
@@ -40,7 +85,7 @@ static inline bool read_integer(uint32_t *result, const char *str, const char *e
             if (*str < '0' || *str > '9')
                 return false;
             value = (value * 10) + (*str - '0');
-            if (value >= UINT32_MAX)
+            if (value > UINT32_MAX)
                 return false;
             str++;
         }
@@ -51,59 +96,29 @@ static inline bool read_integer(uint32_t *result, const char *str, const char *e
 }
 
 /*
-    Read in a boolean argument from the given line and store it in *result.
+    Read in a 16-bit int argument from the given line and store it in *result.
 
-    auto_val is used if the argument's value is "auto". Return true on success
-    and false on failure; in the latter case, *result is not modified.
+    Return true on success and false on failure; in the latter case, *result is
+    not modified.
 */
-bool parse_bool(bool *result, const ASMLine *line, const char *directive, bool auto_val)
+bool parse_uint16(uint16_t *result, const ASMLine *line, const char *directive)
 {
-    const char *arg = line->data + (DIRECTIVE_OFFSET(line, directive) + 1);
-    ssize_t len = line->length - (DIRECTIVE_OFFSET(line, directive) + 1);
-
-    if (len <= 0 || len > 5)
-        return false;
-
-    switch (len) {
-        case 1:  // 0, 1
-            if (*arg == '0' || *arg == '1')
-                return (*result = *arg - '0'), true;
-            return false;
-        case 2:  // on
-            if (!strncmp(arg, "on", 2))
-                return (*result = true), true;
-            return false;
-        case 3:  // off
-            if (!strncmp(arg, "off", 3))
-                return (*result = false), true;
-            return false;
-        case 4:  // true, auto
-            if (!strncmp(arg, "true", 4))
-                return (*result = true), true;
-            if (!strncmp(arg, "auto", 4))
-                return (*result = auto_val), true;
-            return false;
-        case 5:  // false
-            if (!strncmp(arg, "false", 5))
-                return (*result = false), true;
-            return false;
-    }
+    uint32_t value;
+    if (parse_uint32(&value, line, directive) && value <= UINT16_MAX)
+        return (*result = value), true;
     return false;
 }
 
 /*
-    Read in a 32-bit int argument from the given line and store it in *result.
+    Read in an 8-bit int argument from the given line and store it in *result.
 
     Return true on success and false on failure; in the latter case, *result is
     not modified.
 */
-bool parse_uint32(uint32_t *result, const ASMLine *line, const char *directive)
+bool parse_uint8(uint8_t *result, const ASMLine *line, const char *directive)
 {
-    const char *arg = line->data + (DIRECTIVE_OFFSET(line, directive) + 1);
-    ssize_t len = line->length - (DIRECTIVE_OFFSET(line, directive) + 1);
-
     uint32_t value;
-    if (read_integer(&value, arg, arg + len))
+    if (parse_uint32(&value, line, directive) && value <= UINT8_MAX)
         return (*result = value), true;
     return false;
 }
diff --git a/src/assembler/parse_util.h b/src/assembler/parse_util.h
index 85247bc..db1212b 100644
--- a/src/assembler/parse_util.h
+++ b/src/assembler/parse_util.h
@@ -10,3 +10,5 @@
 
 bool parse_bool(bool*, const ASMLine*, const char*, bool);
 bool parse_uint32(uint32_t*, const ASMLine*, const char*);
+bool parse_uint16(uint16_t*, const ASMLine*, const char*);
+bool parse_uint8(uint8_t*, const ASMLine*, const char*);
diff --git a/src/assembler/preprocessor.c b/src/assembler/preprocessor.c
index 04aa43c..68175fd 100644
--- a/src/assembler/preprocessor.c
+++ b/src/assembler/preprocessor.c
@@ -299,8 +299,9 @@ ErrorInfo* preprocess(AssemblerState *state, const LineBuffer *source)
 
     ASMLine dummy = {.next = state->lines};
     ASMLine *prev, *line = &dummy, *next = state->lines, *condemned = NULL;
+
     const ASMLine *first_optimizer = NULL, *first_checksum = NULL,
-                  *first_product = NULL;
+                  *first_product = NULL, *first_version = NULL;
 
     while ((prev = line, line = next)) {
         next = line->next;
@@ -338,8 +339,11 @@ ErrorInfo* preprocess(AssemblerState *state, const LineBuffer *source)
                 CATCH_DUPES(line, first_product, state->header.product_code, arg)
             }
             else if (IS_DIRECTIVE(line, DIR_ROM_VERSION)) {
-                // TODO
-                // state->header.version            <-- range check
+                REQUIRE_ARG(line, DIR_ROM_VERSION)
+                uint8_t arg;
+                VALIDATE(parse_uint8(&arg, line, DIR_ROM_VERSION))
+                RANGE_CHECK(arg, 0x10)
+                CATCH_DUPES(line, first_version, state->header.version, arg)
             }
             else if (IS_DIRECTIVE(line, DIR_ROM_REGION)) {
                 // TODO