diff --git a/lib/headers.c b/lib/headers.c
index b3904cae56..380e3a2c99 100644
--- a/lib/headers.c
+++ b/lib/headers.c
@@ -215,7 +215,7 @@ static CURLcode namevalue(char *header, size_t hlen, unsigned int type,
   *value = header;
 
   /* skip all trailing space letters */
-  while((end > header) && ISSPACE(*end))
+  while((end > header) && ISBLANK(*end))
     *end-- = 0; /* nul terminate */
   return CURLE_OK;
 }
diff --git a/lib/http_aws_sigv4.c b/lib/http_aws_sigv4.c
index 169b68416c..345ac0910f 100644
--- a/lib/http_aws_sigv4.c
+++ b/lib/http_aws_sigv4.c
@@ -233,7 +233,7 @@ static CURLcode make_headers(struct Curl_easy *data,
       sep = strchr(l->data, ';');
     if(!sep || (*sep == ':' && !*(sep + 1)))
       continue;
-    for(ptr = sep + 1; ISSPACE(*ptr); ++ptr)
+    for(ptr = sep + 1; ISBLANK(*ptr); ++ptr)
       ;
     if(!*ptr && ptr != sep + 1) /* a value of whitespace only */
       continue;