diff --git a/df/estimate-max-threads.c b/df/estimate-max-threads.c
index 7d5b09045..ca1fd4264 100644
--- a/df/estimate-max-threads.c
+++ b/df/estimate-max-threads.c
@@ -60,7 +60,7 @@ read_line_from (const char *cmd)
 {
   FILE *pp;
   char *ret = NULL;
-  size_t allocsize;
+  size_t allocsize = 0;
 
   pp = popen (cmd, "r");
   if (pp == NULL)
diff --git a/examples/libvirt-auth.c b/examples/libvirt-auth.c
index 699dd8760..8a5db775a 100644
--- a/examples/libvirt-auth.c
+++ b/examples/libvirt-auth.c
@@ -109,7 +109,7 @@ auth_callback (guestfs_h *g,
   size_t i;
   char *prompt;
   char *reply = NULL;
-  size_t allocsize;
+  size_t allocsize = 0;
   char *pass;
   ssize_t len;
   int r;
diff --git a/fuse/test-fuse.c b/fuse/test-fuse.c
index 84d58e81b..6e91d71af 100644
--- a/fuse/test-fuse.c
+++ b/fuse/test-fuse.c
@@ -250,7 +250,7 @@ test_fuse (void)
   fflush (stdout)
   FILE *fp;
   char *line = NULL;
-  size_t len;
+  size_t len = 0;
   struct stat statbuf;
   char buf[128];
   ssize_t r;
diff --git a/p2v/main.c b/p2v/main.c
index 15628ba62..1f8370bc4 100644
--- a/p2v/main.c
+++ b/p2v/main.c
@@ -306,7 +306,7 @@ partition_parent (dev_t part_dev)
 {
   CLEANUP_FCLOSE FILE *fp = NULL;
   CLEANUP_FREE char *path = NULL, *content = NULL;
-  size_t len;
+  size_t len = 0;
   unsigned parent_major, parent_minor;
 
   if (asprintf (&path, "/sys/dev/block/%d:%d/../dev",
@@ -521,7 +521,7 @@ read_cmdline (void)
 {
   CLEANUP_FCLOSE FILE *fp = NULL;
   char *ret = NULL;
-  size_t len;
+  size_t len = 0;
 
   fp = fopen ("/proc/cmdline", "re");
   if (fp == NULL) {