diff --git a/include/arm9/firm.h b/include/arm9/firm.h
index c405b10..1d91cf4 100644
--- a/include/arm9/firm.h
+++ b/include/arm9/firm.h
@@ -52,7 +52,7 @@
 {
 #endif
 
-bool firm_size(size_t *size);
+bool firm_size(size_t *size, const firm_header *const hdr);
 s32 loadVerifyFirm(const char *const path, bool skipHashCheck, bool installMode);
 noreturn void firmLaunch(void);
 
diff --git a/source/arm9/firm.c b/source/arm9/firm.c
index f6f618f..f21a40c 100644
--- a/source/arm9/firm.c
+++ b/source/arm9/firm.c
@@ -85,9 +85,8 @@
 
 
 /* Calculates the actual firm partition size by using its header */
-bool firm_size(size_t *size)
+bool firm_size(size_t *size, const firm_header *const hdr)
 {
-	firm_header *firm_hdr = (firm_header*)FIRM_LOAD_ADDR;
 	u32 curLen = sizeof(firm_header);
 	u32 curOffset = 0;
 	*size = 0;
@@ -95,7 +94,7 @@
 	/* scan sections in reverse order */
 	for(int i=3; i>=0; i--)
 	{
-		firm_sectionheader *section = &firm_hdr->section[i];
+		const firm_sectionheader *const section = &hdr->section[i];
 
 		if(section->size == 0)
 			continue;
@@ -201,7 +200,7 @@
 		if(!partitionGetSectorOffset(partInd, &sector)) return -3;
 
 		if(!dev_decnand->read_sector(sector, 1, (void*)FIRM_LOAD_ADDR)) return -4;
-		if(!firm_size((size_t*)&firmSize)) return -5;
+		if(!firm_size((size_t*)&firmSize, firmHdr)) return -5;
 		sector++;
 		if(!dev_decnand->read_sector(sector, (firmSize>>9) - 1, (void*)(FIRM_LOAD_ADDR + sizeof(firm_header))))
 			return -4;
@@ -211,7 +210,7 @@
 		firm_header *const ramBootHdr = (firm_header*)RAM_FIRM_BOOT_ADDR;
 		if(memcmp(&ramBootHdr->magic, "FIRM", 4) == 0)
 		{
-			if(!firm_size((size_t*)&firmSize)) return -5;
+			if(!firm_size((size_t*)&firmSize, ramBootHdr)) return -5;
 			NDMA_copy((u32*)FIRM_LOAD_ADDR, (u32*)RAM_FIRM_BOOT_ADDR, firmSize);
 			ramBootHdr->magic = 0;
 		}
diff --git a/source/arm9/firmwriter.c b/source/arm9/firmwriter.c
index 12a6634..2cbb2be 100644
--- a/source/arm9/firmwriter.c
+++ b/source/arm9/firmwriter.c
@@ -86,7 +86,7 @@
 	if(!partitionGetSectorOffset(partInd, &sector)) return -4;
 
 	size_t firmSize;
-	if(!firm_size(&firmSize)) return -5;
+	if(!firm_size(&firmSize, (firm_header*)FIRM_LOAD_ADDR)) return -5;
 
 	u8 *firmBuf = (u8*)FIRM_LOAD_ADDR;
 	if(replaceSig)