diff --git a/src/mars_patcher/constants/credits.py b/src/mars_patcher/constants/credits.py
new file mode 100644
index 0000000..ce6a97d
--- /dev/null
+++ b/src/mars_patcher/constants/credits.py
@@ -0,0 +1,43 @@
+from enum import Enum
+
+
+class LineType(Enum):
+    BLANK = 0
+    BLUE = 1
+    RED = 2
+    WHITE1 = 3
+    WHITE2 = 4
+    COPYRIGHT1 = 5
+    COPYRIGHT2 = 6
+    COPYRIGHT3 = 7
+    COPYRIGHT4 = 8
+    END = 9
+
+
+LINE_TYPE_VALS = {
+    LineType.BLANK: 0x5,
+    LineType.BLUE: 0x0,
+    LineType.RED: 0x1,
+    LineType.WHITE1: 0x3,
+    LineType.WHITE2: 0x2,
+    LineType.COPYRIGHT1: 0xA,
+    LineType.COPYRIGHT2: 0xB,
+    LineType.COPYRIGHT3: 0xC,
+    LineType.COPYRIGHT4: 0xD,
+    LineType.END: 0x6,
+}
+
+LINE_TYPE_HEIGHTS = {
+    LineType.BLANK: 1,
+    LineType.BLUE: 1,
+    LineType.RED: 1,
+    LineType.WHITE1: 1,
+    LineType.WHITE2: 2,
+    LineType.COPYRIGHT1: 1,
+    LineType.COPYRIGHT2: 1,
+    LineType.COPYRIGHT3: 1,
+    LineType.COPYRIGHT4: 1,
+    LineType.END: 0,
+}
+
+TEXT_LINE_TYPES = {LineType.BLUE, LineType.RED, LineType.WHITE1, LineType.WHITE2}
diff --git a/src/mars_patcher/credits.py b/src/mars_patcher/credits.py
index 6c6f460..bd79d58 100644
--- a/src/mars_patcher/credits.py
+++ b/src/mars_patcher/credits.py
@@ -1,17 +1,12 @@
-from mars_patcher.mf.auto_generated_types import MarsschemamfCreditstextItem
-from mars_patcher.mf.constants.credits_lines import (
-    FUSION_STAFF_LINES,
+from mars_patcher.constants.credits import (
     LINE_TYPE_HEIGHTS,
     LINE_TYPE_VALS,
-    MARS_CREDITS,
-    RDV_CREDITS,
     TEXT_LINE_TYPES,
     LineType,
 )
+from mars_patcher.mf.auto_generated_types import MarsschemamfCreditstextItem
 from mars_patcher.rom import Rom
 
-CREDITS_ADDR = 0x74B0B0
-CREDITS_LEN = 0x2B98
 FULL_LINE_LEN = 36
 LINE_WIDTH = 30
 
@@ -46,26 +41,10 @@ def from_json(cls, data: MarsschemamfCreditstextItem) -> "CreditsLine":
         return CreditsLine(line_type, blank_lines, text, centered)
 
 
-def write_credits(rom: Rom, data: list[MarsschemamfCreditstextItem]) -> None:
-    writer = CreditsWriter(rom)
-    # Write MARS credits
-    lines = [CreditsLine(*line) for line in MARS_CREDITS]
-    writer.write_lines(lines)
-    # Write RDV credits
-    lines = [CreditsLine(*line) for line in RDV_CREDITS]
-    writer.write_lines(lines)
-    # Write custom credits
-    lines = [CreditsLine.from_json(d) for d in data]
-    writer.write_lines(lines)
-    # Write fusion staff credits
-    lines = [CreditsLine(*line) for line in FUSION_STAFF_LINES]
-    writer.write_lines(lines)
-
-
 class CreditsWriter:
-    def __init__(self, rom: Rom):
+    def __init__(self, rom: Rom, addr: int):
         self.rom = rom
-        self.addr = CREDITS_ADDR
+        self.addr = addr
         self.num_lines = 0
 
     def write_lines(self, lines: list[CreditsLine]) -> None:
diff --git a/src/mars_patcher/mf/constants/credits_lines.py b/src/mars_patcher/mf/constants/credits_lines.py
index 85a8cf2..4380eb5 100644
--- a/src/mars_patcher/mf/constants/credits_lines.py
+++ b/src/mars_patcher/mf/constants/credits_lines.py
@@ -1,46 +1,4 @@
-from enum import Enum
-
-
-class LineType(Enum):
-    BLANK = 0
-    BLUE = 1
-    RED = 2
-    WHITE1 = 3
-    WHITE2 = 4
-    COPYRIGHT1 = 5
-    COPYRIGHT2 = 6
-    COPYRIGHT3 = 7
-    COPYRIGHT4 = 8
-    END = 9
-
-
-LINE_TYPE_VALS = {
-    LineType.BLANK: 0x5,
-    LineType.BLUE: 0x0,
-    LineType.RED: 0x1,
-    LineType.WHITE1: 0x3,
-    LineType.WHITE2: 0x2,
-    LineType.COPYRIGHT1: 0xA,
-    LineType.COPYRIGHT2: 0xB,
-    LineType.COPYRIGHT3: 0xC,
-    LineType.COPYRIGHT4: 0xD,
-    LineType.END: 0x6,
-}
-
-LINE_TYPE_HEIGHTS = {
-    LineType.BLANK: 1,
-    LineType.BLUE: 1,
-    LineType.RED: 1,
-    LineType.WHITE1: 1,
-    LineType.WHITE2: 2,
-    LineType.COPYRIGHT1: 1,
-    LineType.COPYRIGHT2: 1,
-    LineType.COPYRIGHT3: 1,
-    LineType.COPYRIGHT4: 1,
-    LineType.END: 0,
-}
-
-TEXT_LINE_TYPES = {LineType.BLUE, LineType.RED, LineType.WHITE1, LineType.WHITE2}
+from mars_patcher.constants.credits import LineType
 
 MARS_CREDITS = [
     (LineType.WHITE2, 4, "MARS Development"),
diff --git a/src/mars_patcher/mf/credits.py b/src/mars_patcher/mf/credits.py
new file mode 100644
index 0000000..cea23f0
--- /dev/null
+++ b/src/mars_patcher/mf/credits.py
@@ -0,0 +1,30 @@
+from mars_patcher.credits import CreditsLine, CreditsWriter
+from mars_patcher.mf.auto_generated_types import MarsschemamfCreditstextItem
+from mars_patcher.mf.constants.credits_lines import (
+    FUSION_STAFF_LINES,
+    MARS_CREDITS,
+    RDV_CREDITS,
+)
+from mars_patcher.rom import Rom
+
+CREDITS_ADDR = 0x74B0B0
+CREDITS_LEN = 0x2B98
+
+
+def write_credits(rom: Rom, data: list[MarsschemamfCreditstextItem]) -> None:
+    writer = CreditsWriter(rom, CREDITS_ADDR)
+    # Write MARS credits
+    lines = [CreditsLine(*line) for line in MARS_CREDITS]
+    writer.write_lines(lines)
+    # Write RDV credits
+    lines = [CreditsLine(*line) for line in RDV_CREDITS]
+    writer.write_lines(lines)
+    # Write custom credits
+    lines = [CreditsLine.from_json(d) for d in data]
+    writer.write_lines(lines)
+    # Write fusion staff credits
+    lines = [CreditsLine(*line) for line in FUSION_STAFF_LINES]
+    writer.write_lines(lines)
+    # Verify that credits don't exceed existing space
+    if writer.addr > CREDITS_ADDR + CREDITS_LEN:
+        raise ValueError("Credits exceeded existing space")
diff --git a/src/mars_patcher/mf/patcher.py b/src/mars_patcher/mf/patcher.py
index 19a2816..9234dec 100644
--- a/src/mars_patcher/mf/patcher.py
+++ b/src/mars_patcher/mf/patcher.py
@@ -1,10 +1,10 @@
 from collections.abc import Callable
 from os import PathLike
 
-from mars_patcher.credits import write_credits
 from mars_patcher.level_edits import apply_level_edits
 from mars_patcher.mf.auto_generated_types import MarsSchemaMF
 from mars_patcher.mf.connections import Connections
+from mars_patcher.mf.credits import write_credits
 from mars_patcher.mf.door_locks import set_door_locks
 from mars_patcher.mf.item_patcher import (
     ItemPatcher,