diff --git a/config.c b/config.c
index a850b617..8a7a3476 100644
--- a/config.c
+++ b/config.c
@@ -427,7 +427,7 @@ parse_section_scrollback(const char *key, const char *value, struct config *conf
             conf->scrollback.indicator.text = NULL;
 
             size_t len = mbstowcs(NULL, value, 0);
-            if (len < 0) {
+            if (len == (size_t)-1) {
                 LOG_AND_NOTIFY_ERRNO(
                     "%s:%d: [scrollback]: indicator-format: "
                     "invalid value: %s", path, lineno, value);
diff --git a/shm.c b/shm.c
index 2b2c3435..8a0a136d 100644
--- a/shm.c
+++ b/shm.c
@@ -131,10 +131,12 @@ page_size(void)
 {
     static size_t size = 0;
     if (size == 0) {
-        size = sysconf(_SC_PAGE_SIZE);
-        if (size < 0) {
+        long n = sysconf(_SC_PAGE_SIZE);
+        if (n <= 0) {
             LOG_ERRNO("failed to get page size");
             size = 4096;
+        } else {
+            size = (size_t)n;
         }
     }
     assert(size > 0);