diff --git a/auth.c b/auth.c
index da0c0294..361f656c 100644
--- a/auth.c
+++ b/auth.c
@@ -150,8 +150,8 @@ static int parse_auth_choice(struct openconnect_info *vpninfo, struct oc_auth_fo
 			continue;
 
 		opt->nr_choices++;
-		opt = realloc(opt, sizeof(*opt) +
-				   opt->nr_choices * sizeof(*choice));
+		realloc_inplace(opt, sizeof(*opt) +
+				opt->nr_choices * sizeof(*choice));
 		if (!opt)
 			return -ENOMEM;
 
diff --git a/compat.c b/compat.c
index da59d359..d728c94c 100644
--- a/compat.c
+++ b/compat.c
@@ -131,7 +131,7 @@ ssize_t openconnect__getline(char **lineptr, size_t *n, FILE *stream)
 			break;
 
 		*n *= 2;
-		*lineptr = realloc(*lineptr, *n);
+		realloc_inplace(*lineptr, *n);
 		if (!*lineptr)
 			return -1;
 	}
diff --git a/http.c b/http.c
index d6a3636c..9b77be58 100644
--- a/http.c
+++ b/http.c
@@ -96,7 +96,7 @@ static void buf_append(struct oc_text_buf *buf, const char *fmt, ...)
 				break;
 			}
 
-			buf->data = realloc(buf->data, new_buf_len);
+			realloc_inplace(buf->data, new_buf_len);
 			if (!buf->data) {
 				buf->error = -ENOMEM;
 				break;
@@ -353,7 +353,7 @@ static int process_http_response(struct openconnect_info *vpninfo, int *result,
 				lastchunk = 1;
 				goto skip;
 			}
-			body = realloc(body, done + chunklen + 1);
+			realloc_inplace(body, done + chunklen + 1);
 			if (!body)
 				return -ENOMEM;
 			while (chunklen) {
@@ -394,7 +394,7 @@ static int process_http_response(struct openconnect_info *vpninfo, int *result,
 
 		/* HTTP 1.0 response. Just eat all we can in 16KiB chunks */
 		while (1) {
-			body = realloc(body, done + 16384);
+			realloc_inplace(body, done + 16384);
 			if (!body)
 				return -ENOMEM;
 			i = openconnect_SSL_read(vpninfo, body + done, 16384);
@@ -407,7 +407,7 @@ static int process_http_response(struct openconnect_info *vpninfo, int *result,
 				return i;
 			} else {
 				/* Connection closed. Reduce allocation to just what we need */
-				body = realloc(body, done + 1);
+				realloc_inplace(body, done + 1);
 				if (!body)
 					return -ENOMEM;
 				break;
diff --git a/openconnect-internal.h b/openconnect-internal.h
index 4b4c4550..ff1b80bf 100644
--- a/openconnect-internal.h
+++ b/openconnect-internal.h
@@ -347,6 +347,14 @@ ssize_t openconnect__getline(char **lineptr, size_t *n, FILE *stream);
 char *openconnect__strcasestr(const char *haystack, const char *needle);
 #endif
 
+/* I always coded as if it worked like this. Now it does. */
+#define realloc_inplace(p, size) do {			\
+	void *__realloc_old = p;			\
+	p = realloc(p, size);				\
+	if (size && !p)					\
+		free(__realloc_old);			\
+    } while (0)
+
 /****************************************************************************/
 
 /* tun.c */