diff --git a/ggsn/ggsn_vty.c b/ggsn/ggsn_vty.c
index fd2c6ad..f76018e 100644
--- a/ggsn/ggsn_vty.c
+++ b/ggsn/ggsn_vty.c
@@ -899,7 +899,7 @@ DEFUN(show_pdpctx_imsi, show_pdpctx_imsi_cmd,
 		return CMD_WARNING;
 	}
 
-	imsi = imsi_str2gtp(argv[1]);
+	imsi = gtp_imsi_str2gtp(argv[1]);
 
 	if (argc > 2) {
 		nsapi = atoi(argv[2]);
diff --git a/gtp/gtp.c b/gtp/gtp.c
index d4c83d9..25eafdf 100644
--- a/gtp/gtp.c
+++ b/gtp/gtp.c
@@ -3493,16 +3493,25 @@ const char *imsi_gtp2str(const uint64_t *imsi)
 	return buf;
 }
 
-/* Encode an IMSI with gtp encoding according to TS 29.060 - the
-   reverse of imsi_gtp2str(). The hash index used for context
-   lookups is generated from the IMSI in gtp format. User input
-   in the vty (for example) needs to be converted to match. */
-const uint64_t imsi_str2gtp(const char *imsi)
+/* Generate the GTP IMSI IE according to 09.60 Section 7.9.2 */
+uint64_t gtp_imsi_str2gtp(const char *str)
 {
-	uint64_t ret = 0xf000000000000000ull;
-	unsigned int i, imsi_length = strlen(imsi);
+	uint64_t imsi64 = 0;
+	unsigned int n;
+	unsigned int imsi_len = strlen(str);
 
-	for (i = 0; i < imsi_length; i++)
-		ret |= ((uint64_t) (imsi[i] - '0')) << (i * 4);
-	return ret;
-}
\ No newline at end of file
+	if (imsi_len > 16) {
+		LOGP(DLGTP, LOGL_NOTICE, "IMSI length > 16 not supported!\n");
+		return 0;
+	}
+
+	for (n = 0; n < 16; n++) {
+		uint64_t val;
+		if (n < imsi_len)
+			val = (str[n]-'0') & 0xf;
+		else
+			val = 0xf;
+		imsi64 |= (val << (n*4));
+	}
+	return imsi64;
+}
diff --git a/gtp/gtp.h b/gtp/gtp.h
index 95566fa..45eb285 100644
--- a/gtp/gtp.h
+++ b/gtp/gtp.h
@@ -441,6 +441,6 @@ extern int eua2ipv4(struct in_addr *dst, struct ul66_t *eua);
 extern int gsna2in_addr(struct in_addr *dst, struct ul16_t *gsna);
 extern int in_addr2gsna(struct ul16_t *gsna, struct in_addr *src);
 extern const char *imsi_gtp2str(const uint64_t *imsi);
-extern const uint64_t imsi_str2gtp(const char *imsi);
+extern uint64_t gtp_imsi_str2gtp(const char *str);
 
 #endif /* !_GTP_H */
diff --git a/sgsnemu/sgsnemu.c b/sgsnemu/sgsnemu.c
index 002c2e4..7893f4f 100644
--- a/sgsnemu/sgsnemu.c
+++ b/sgsnemu/sgsnemu.c
@@ -497,7 +497,7 @@ static int process_options(int argc, char **argv)
 		return -1;
 	}
 
-	options.imsi = imsi_str2gtp(args_info.imsi_arg);
+	options.imsi = gtp_imsi_str2gtp(args_info.imsi_arg);
 
 	printf("IMSI is:               %s (%#08llx)\n",
 	       args_info.imsi_arg, options.imsi);