diff --git a/src/disk_tool/disk_tool.h b/src/disk_tool/disk_tool.h
index 1853cdf6..0aceab06 100644
--- a/src/disk_tool/disk_tool.h
+++ b/src/disk_tool/disk_tool.h
@@ -175,7 +175,6 @@ struct disk_tool_t
 void disk_tool_simple_offsets(json11::Json cfg, bool json_output);
 
 uint64_t sscanf_json(const char *fmt, const json11::Json & str);
-void fromhexstr(const std::string & from, int bytes, uint8_t *to);
 int disable_cache(const std::string & dev);
 uint64_t get_atomic_write_size(const std::string & dev);
 uint64_t get_device_size(const std::string & dev, bool should_exist = false);
diff --git a/src/disk_tool/disk_tool_journal.cpp b/src/disk_tool/disk_tool_journal.cpp
index 1d10ef37..3e6199b4 100644
--- a/src/disk_tool/disk_tool_journal.cpp
+++ b/src/disk_tool/disk_tool_journal.cpp
@@ -4,6 +4,7 @@
 #include <unistd.h>
 
 #include "disk_tool.h"
+#include "str_util.h"
 #include "malloc_or_die.h"
 
 int disk_tool_t::dump_journal()
diff --git a/src/disk_tool/disk_tool_meta.cpp b/src/disk_tool/disk_tool_meta.cpp
index 814603a8..e07d4f34 100644
--- a/src/disk_tool/disk_tool_meta.cpp
+++ b/src/disk_tool/disk_tool_meta.cpp
@@ -4,6 +4,7 @@
 #include "disk_tool.h"
 #include "rw_blocking.h"
 #include "json_util.h"
+#include "str_util.h"
 #include "malloc_or_die.h"
 
 int disk_tool_t::process_meta(std::function<void(blockstore_meta_header_v3_t *)> hdr_fn,
diff --git a/src/disk_tool/disk_tool_utils.cpp b/src/disk_tool/disk_tool_utils.cpp
index 142c3048..a6c5e431 100644
--- a/src/disk_tool/disk_tool_utils.cpp
+++ b/src/disk_tool/disk_tool_utils.cpp
@@ -22,28 +22,6 @@ uint64_t sscanf_json(const char *fmt, const json11::Json & str)
     return value;
 }
 
-static int fromhex(char c)
-{
-    if (c >= '0' && c <= '9')
-        return (c-'0');
-    else if (c >= 'a' && c <= 'f')
-        return (c-'a'+10);
-    else if (c >= 'A' && c <= 'F')
-        return (c-'A'+10);
-    return -1;
-}
-
-void fromhexstr(const std::string & from, int bytes, uint8_t *to)
-{
-    for (int i = 0; i < from.size() && i < bytes; i++)
-    {
-        int x = fromhex(from[2*i]), y = fromhex(from[2*i+1]);
-        if (x < 0 || y < 0)
-            break;
-        to[i] = x*16 + y;
-    }
-}
-
 // returns 1 = check error, 0 = write through, -1 = write back
 // (similar to 1 = warning, -1 = error, 0 = success in disable_cache)
 static int check_queue_cache(std::string dev, std::string parent_dev)
diff --git a/src/util/str_util.cpp b/src/util/str_util.cpp
index 74649665..c0cf8543 100644
--- a/src/util/str_util.cpp
+++ b/src/util/str_util.cpp
@@ -504,7 +504,7 @@ bool is_zero(void *buf, size_t size)
     return true;
 }
 
-char hextochar(char h)
+static uint8_t fromhexchar(char h, uint8_t def)
 {
     if (h >= 'a' && h <= 'f')
         return h-'a'+10;
@@ -512,7 +512,7 @@ char hextochar(char h)
         return h-'A'+10;
     else if (h >= '0' && h <= '9')
         return h-'0';
-    return 0;
+    return def;
 }
 
 std::string urldecode(const std::string & orig)
@@ -526,7 +526,7 @@ std::string urldecode(const std::string & orig)
             res.push_back(' ');
         else if (orig[i] == '%' && i < len-2)
         {
-            res.push_back(hextochar(orig[i+1])*16 + hextochar(orig[i+2]));
+            res.push_back(fromhexchar(orig[i+1], 0)*16 + fromhexchar(orig[i+2], 0));
             i += 2;
         }
         else
@@ -534,3 +534,20 @@ std::string urldecode(const std::string & orig)
     }
     return res;
 }
+
+size_t fromhexstr(const std::string & from, size_t bytes, uint8_t *to)
+{
+    if (bytes > from.size()/2)
+        bytes = from.size()/2;
+    size_t i = 0;
+    while (i < bytes)
+    {
+        uint8_t x = fromhexchar(from[2*i], 16);
+        uint8_t y = fromhexchar(from[2*i+1], 16);
+        if (x == 16 || y == 16)
+            break;
+        to[i] = x*16 + y;
+        i++;
+    }
+    return i;
+}
diff --git a/src/util/str_util.h b/src/util/str_util.h
index 463cc628..4ae01f35 100644
--- a/src/util/str_util.h
+++ b/src/util/str_util.h
@@ -35,5 +35,6 @@ std::string realpath_str(std::string path, bool nofail = true);
 std::string format_datetime(uint64_t unixtime);
 bool is_zero(void *buf, size_t size);
 std::string urldecode(const std::string & orig);
+size_t fromhexstr(const std::string & from, size_t bytes, uint8_t *to);
 
 #pragma GCC visibility pop