diff --git a/corelib/server_utils.c b/corelib/server_utils.c
index 2b3c64e3..9c9265e2 100644
--- a/corelib/server_utils.c
+++ b/corelib/server_utils.c
@@ -4,6 +4,7 @@
  *
  * SPDX-License-Identifier:     GPL-2.0-only
  */
+#include <errno.h>
 #include <unistd.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -24,8 +25,11 @@ int channel_settings(void *elem, void *data)
 		&chan->retries);
 
 	GET_FIELD_STRING_RESET(LIBCFG_PARSER, elem, "max-download-speed", tmp);
-	if (strlen(tmp))
+	if (strlen(tmp)) {
 		chan->max_download_speed = (unsigned int)ustrtoull(tmp, NULL, 10);
+		if (errno)
+			WARN("max-download-speed setting %s: ustrtoull failed", tmp);
+	}
 
 	GET_FIELD_STRING_RESET(LIBCFG_PARSER, elem, "retrywait", tmp);
 	if (strlen(tmp))
diff --git a/handlers/copy_handler.c b/handlers/copy_handler.c
index abf65bd3..3e2f1f40 100644
--- a/handlers/copy_handler.c
+++ b/handlers/copy_handler.c
@@ -204,9 +204,10 @@ static int recurse_directory(const char *fpath, const struct stat *sb,
 static int copy_image_file(struct img_type *img, void *data)
 {
 	int ret = 0;
+	char *tmp;
 	struct dict_list *proplist;
 	struct dict_list_elem *entry;
-	size_t size;
+	size_t size = 0;
 	struct script_handler_data *script_data;
 	bool recursive, createdest;
 
@@ -249,7 +250,12 @@ static int copy_image_file(struct img_type *img, void *data)
 	/*
 	 * Detect the size if not set in sw-descriptiont
 	 */
-	size = dict_get_value(&img->properties, "size") ? ustrtoull(dict_get_value(&img->properties, "size"), NULL, 0) : 0;
+	tmp = dict_get_value(&img->properties, "size");
+	if (tmp) {
+		size = ustrtoull(tmp, NULL, 0);
+		if (errno)
+			WARN("size property %s: ustrtoull failed", tmp);
+	}
 
 	/*
 	 * No chain set, fallback to rawcopy
diff --git a/handlers/delta_handler.c b/handlers/delta_handler.c
index 89160036..8e7faa0e 100644
--- a/handlers/delta_handler.c
+++ b/handlers/delta_handler.c
@@ -326,10 +326,13 @@ static int delta_retrieve_attributes(struct img_type *img, struct hnd_priv *priv
 	char *srcsize;
 	srcsize = dict_get_value(&img->properties, "source-size");
 	if (srcsize) {
-		if (!strcmp(srcsize, "detect"))
+		if (!strcmp(srcsize, "detect")) {
 			priv->detectsrcsize = true;
-		else
+		} else {
 			priv->srcsize = ustrtoull(srcsize, NULL, 10);
+			if (errno)
+				WARN("source-size %s: ustrotull failed", srcsize);
+		}
 	}
 
 	char *zckloglevel = dict_get_value(&img->properties, "zckloglevel");
diff --git a/handlers/diskpart_handler.c b/handlers/diskpart_handler.c
index 4c2b902b..982c494e 100644
--- a/handlers/diskpart_handler.c
+++ b/handlers/diskpart_handler.c
@@ -1232,11 +1232,15 @@ static int diskpart(struct img_type *img,
 					switch (i) {
 					case PART_SIZE:
 						part->size = ustrtoull(equal, NULL, 10);
+						if (errno)
+							WARN("partition size %s: ustrtoull failed", equal);
 						if (!size_delimiter_match(equal))
 							part->explicit_size = 1;
 						break;
 					case PART_START:
 						part->start = ustrtoull(equal, NULL, 10);
+						if (errno)
+							WARN("partition size %s: ustrtoull failed", equal);
 						break;
 					case PART_TYPE:
 						strncpy(part->type, equal, sizeof(part->type));
diff --git a/suricatta/server_general.c b/suricatta/server_general.c
index 5c51fda6..db5a60ae 100644
--- a/suricatta/server_general.c
+++ b/suricatta/server_general.c
@@ -663,6 +663,11 @@ static server_op_res_t server_start(const char *fname, int argc, char *argv[])
 		case 'n':
 			channel_data_defaults.max_download_speed =
 				(unsigned int)ustrtoull(optarg, NULL, 10);
+			if (errno) {
+				ERROR("max-download-speed %s: ustrtoull failed",
+				      optarg);
+				return SERVER_EINIT;
+			}
 			break;
 
 		/* Ignore the --server option which is already parsed by the caller. */
diff --git a/suricatta/server_hawkbit.c b/suricatta/server_hawkbit.c
index 3c38ea61..9c3e9741 100644
--- a/suricatta/server_hawkbit.c
+++ b/suricatta/server_hawkbit.c
@@ -871,6 +871,9 @@ static void get_action_id_from_env(int *action_id)
 	char *action_str = swupdate_vars_get("action_id", NULL);
 	if (action_str) {
 		int tmp = ustrtoull(action_str, NULL, 10);
+		if (errno)
+			WARN("action_id %s: ustrtoull failed",
+			     action_str);
 		/*
 		 * action_id = 0 is invalid, then check it
 		 */
@@ -1910,6 +1913,11 @@ static server_op_res_t server_start(const char *fname, int argc, char *argv[])
 		case 'n':
 			channel_data_defaults.max_download_speed =
 				(unsigned int)ustrtoull(optarg, NULL, 10);
+			if (errno) {
+				ERROR("max-download-speed %s: ustrtoull failed",
+				      optarg);
+				return SERVER_EINIT;
+			}
 			break;
 		/* Ignore not recognized options, they can be already parsed by the caller */
 		case '?':
diff --git a/suricatta/server_lua.c b/suricatta/server_lua.c
index f5b90f6d..c749c1c5 100644
--- a/suricatta/server_lua.c
+++ b/suricatta/server_lua.c
@@ -591,6 +591,9 @@ static void channel_set_options(lua_State *L, channel_data_t *channel_data)
 	get_from_table(L, "max_download_speed", max_download_speed);
 	if (max_download_speed) {
 		channel_data->max_download_speed = (unsigned int)ustrtoull(max_download_speed, NULL, 10);
+		if (errno)
+			WARN("max-download-speed %s: ustrtoull failed",
+			     max_download_speed);
 		free(max_download_speed);
 	}
 	lua_getfield(L, -1, "proxy");