diff --git a/zdump/df_elf.c b/zdump/df_elf.c
index 257ffaa9..626f35be 100644
--- a/zdump/df_elf.c
+++ b/zdump/df_elf.c
@@ -74,10 +74,13 @@ Elf64_Phdr *read_elf_phdrs(const struct zg_fh *fh, const Elf64_Ehdr *ehdr, unsig
 		return NULL;
 	}
 
+	if (ehdr->e_phoff > OFF_T_MAX)
+		ERR_EXIT("Unsupported offset");
+
 	/* Cannot wraparound since `Elf64_Half`` is `uint16_t` */
 	phdrs_size = sizeof(*phdrs) * phnum;
 	phdrs = util_malloc(phdrs_size);
-	zg_seek(fh, ehdr->e_phoff, ZG_CHECK);
+	zg_seek(fh, (off_t)ehdr->e_phoff, ZG_CHECK);
 	zg_read(fh, phdrs, phdrs_size, ZG_CHECK);
 	*phdr_count = phnum;
 	return phdrs;
diff --git a/zdump/zg.h b/zdump/zg.h
index 977d27c3..d4f3d62b 100644
--- a/zdump/zg.h
+++ b/zdump/zg.h
@@ -16,6 +16,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
@@ -31,6 +32,8 @@
 #define U32_MAX	((u32) -1)
 #define U16_MAX	((u16) -1)
 #define U8_MAX	((u8) -1)
+#define OFF_T_MAX LONG_MAX
+STATIC_ASSERT(sizeof(off_t) == sizeof(long))
 
 /*
  * IEC definitions