diff --git a/src/exports/pe_get_export_symbol_info.c b/src/exports/pe_get_export_symbol_info.c
index 9f00634..4f9f5c6 100644
--- a/src/exports/pe_get_export_symbol_info.c
+++ b/src/exports/pe_get_export_symbol_info.c
@@ -23,7 +23,7 @@ int pe_get_export_symbol_info(
 {
 	struct pe_export_hdr *	exp_hdr;
 
-	size_t		len;
+	ssize_t		len;
 	uint32_t *	rva_offset;
 	uintptr_t *	addr_offset;
 
diff --git a/src/internal/pe_impl.c b/src/internal/pe_impl.c
index 2611f6b..594f23d 100644
--- a/src/internal/pe_impl.c
+++ b/src/internal/pe_impl.c
@@ -8,7 +8,7 @@
 #include <pemagine/pemagine.h>
 #include "pe_impl.h"
 
-uint32_t pe_impl_strlen_ansi(const char * str)
+int32_t pe_impl_strlen_ansi(const char * str)
 {
 	char * ch;
 	char * upper_bound;
@@ -25,7 +25,7 @@ uint32_t pe_impl_strlen_ansi(const char * str)
 }
 
 
-uint32_t pe_impl_strlen_utf16(const wchar16_t * str)
+int32_t pe_impl_strlen_utf16(const wchar16_t * str)
 {
 	wchar16_t *	wch;
 	wchar16_t *	upper_bound;
diff --git a/src/internal/pe_impl.h b/src/internal/pe_impl.h
index 392f6b2..43ec6ef 100644
--- a/src/internal/pe_impl.h
+++ b/src/internal/pe_impl.h
@@ -12,6 +12,6 @@ struct pe_block {
 	uint32_t	size;
 };
 
-uint32_t	pe_impl_strlen_ansi(const char * str);
-uint32_t	pe_impl_strlen_utf16(const wchar16_t * str);
+int32_t		pe_impl_strlen_ansi(const char * str);
+int32_t		pe_impl_strlen_utf16(const wchar16_t * str);
 wchar16_t	pe_impl_utf16_char_to_lower(const wchar16_t c);