diff --git a/mongoose.c b/mongoose.c
index e32264803d..12569e41b7 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -3159,6 +3159,7 @@ static int skip_chunk(const char *buf, int len, int *pl, int *dl) {
   int i = 0, n = 0;
   if (len < 3) return 0;
   while (i < len && is_hex_digit(buf[i])) i++;
+  if (i == 0) return -1;                     // Error, no length specified
   if (i > (int) sizeof(int) * 2) return -1;  // Chunk length is too big
   if (len < i + 1 || buf[i] != '\r' || buf[i + 1] != '\n') return -1;  // Error
   n = (int) mg_unhexn(buf, (size_t) i);  // Decode chunk length
diff --git a/src/http.c b/src/http.c
index 16608089a0..b7c85ff0b1 100644
--- a/src/http.c
+++ b/src/http.c
@@ -1,7 +1,7 @@
-#include "http.h"
 #include "arch.h"
 #include "base64.h"
 #include "fmt.h"
+#include "http.h"
 #include "json.h"
 #include "log.h"
 #include "net.h"
@@ -962,6 +962,7 @@ static int skip_chunk(const char *buf, int len, int *pl, int *dl) {
   int i = 0, n = 0;
   if (len < 3) return 0;
   while (i < len && is_hex_digit(buf[i])) i++;
+  if (i == 0) return -1;                     // Error, no length specified
   if (i > (int) sizeof(int) * 2) return -1;  // Chunk length is too big
   if (len < i + 1 || buf[i] != '\r' || buf[i + 1] != '\n') return -1;  // Error
   n = (int) mg_unhexn(buf, (size_t) i);  // Decode chunk length
diff --git a/test/unit_test.c b/test/unit_test.c
index a219b2a30c..dbc736ca01 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -1161,6 +1161,22 @@ static void test_http_server(void) {
   }
 #endif
 
+  // #2552, reject chunks with no length
+  ASSERT(fetch(&mgr, buf, url,
+               "POST / HTTP/1.1\r\n"
+               "Transfer-Encoding: chunked\r\n\r\n"
+               "1\r\n"
+               "Z\r\n"
+               "?\r\n"
+               "\r\n") == 0);
+  ASSERT(fetch(&mgr, buf, url,
+               "POST / HTTP/1.1\r\n"
+               "Transfer-Encoding: chunked\r\n\r\n"
+               "1\r\n"
+               "Z\r\n"
+               "\r\n"
+               "\r\n") == 0);
+
   mg_mgr_free(&mgr);
   ASSERT(mgr.conns == NULL);
 }
@@ -1605,11 +1621,11 @@ static void test_http_parse(void) {
     ASSERT(mg_http_parse(s, strlen(s), &hm) == (int) strlen(s));
     s = "a\nb:b\nc:c\n\n";
     ASSERT(mg_http_parse(s, strlen(s), &hm) < 0);
-    s = "a b\nc: \xc0\n\n"; // Invalid UTF in the header value: accept
+    s = "a b\nc: \xc0\n\n";  // Invalid UTF in the header value: accept
     ASSERT(mg_http_parse(s, strlen(s), &hm) == (int) strlen(s));
     ASSERT((v = mg_http_get_header(&hm, "c")) != NULL);
     ASSERT(mg_vcmp(v, "\xc0") == 0);
-    s = "a b\n\xc0: 2\n\n"; // Invalid UTF in the header name: do NOT accept
+    s = "a b\n\xc0: 2\n\n";  // Invalid UTF in the header name: do NOT accept
     ASSERT(mg_http_parse(s, strlen(s), &hm) == -1);
   }
 }