diff --git a/modules/ssl/ssl_engine_init.c b/modules/ssl/ssl_engine_init.c
index 8b6c34f..3587fb5 100644
--- a/modules/ssl/ssl_engine_init.c
+++ b/modules/ssl/ssl_engine_init.c
@@ -1609,6 +1609,10 @@ static apr_status_t ssl_init_proxy_certs(server_rec *s,
     STACK_OF(X509) *chain;
     X509_STORE_CTX *sctx;
     X509_STORE *store = SSL_CTX_get_cert_store(mctx->ssl_ctx);
+    int addl_chain = 0; /* non-zero if additional chain certs were
+                         * added to store */
+
+    ap_assert(store != NULL); /* safe to assume always non-NULL? */
 
 #if OPENSSL_VERSION_NUMBER >= 0x1010100fL
     /* For OpenSSL >=1.1.1, turn on client cert support which is
@@ -1653,20 +1657,28 @@ static apr_status_t ssl_init_proxy_certs(server_rec *s,
         }
     }
 
-    if ((ncerts = sk_X509_INFO_num(sk)) <= 0) {
-        sk_X509_INFO_free(sk);
-        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s, APLOGNO(02206)
-                     "no client certs found for SSL proxy");
-        return APR_SUCCESS;
-    }
-
     /* Check that all client certs have got certificates and private
-     * keys. */
-    for (n = 0; n < ncerts; n++) {
+     * keys.  Note the number of certs in the stack may decrease
+     * during the loop. */
+    for (n = 0; n < sk_X509_INFO_num(sk); n++) {
         X509_INFO *inf = sk_X509_INFO_value(sk, n);
+        int has_privkey = inf->x_pkey && inf->x_pkey->dec_pkey;
+
+        /* For a lone certificate in the file, trust it as a
+         * CA/intermediate certificate. */
+        if (inf->x509 && !has_privkey && !inf->enc_data) {
+            ssl_log_xerror(SSLLOG_MARK, APLOG_DEBUG, 0, ptemp, s, inf->x509,
+                           APLOGNO(10261) "Trusting non-leaf certificate");
+            X509_STORE_add_cert(store, inf->x509); /* increments inf->x509 */
+            /* Delete from the stack and iterate again. */
+            X509_INFO_free(inf);
+            sk_X509_INFO_delete(sk, n);
+            n--;
+            addl_chain = 1;
+            continue;
+        }
 
-        if (!inf->x509 || !inf->x_pkey || !inf->x_pkey->dec_pkey ||
-            inf->enc_data) {
+        if (!has_privkey || inf->enc_data) {
             sk_X509_INFO_free(sk);
             ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, s, APLOGNO(02252)
                          "incomplete client cert configured for SSL proxy "
@@ -1683,13 +1695,21 @@ static apr_status_t ssl_init_proxy_certs(server_rec *s,
         }
     }
 
+    if ((ncerts = sk_X509_INFO_num(sk)) <= 0) {
+        sk_X509_INFO_free(sk);
+        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s, APLOGNO(02206)
+                     "no client certs found for SSL proxy");
+        return APR_SUCCESS;
+    }
+
     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(02207)
                  "loaded %d client certs for SSL proxy",
                  ncerts);
     pkp->certs = sk;
 
-
-    if (!pkp->ca_cert_file || !store) {
+    /* If any chain certs are configured, build the ->ca_certs chains
+     * corresponding to the loaded keypairs. */
+    if (!pkp->ca_cert_file && !addl_chain) {
         return APR_SUCCESS;
     }
 
diff --git a/modules/ssl/ssl_private.h b/modules/ssl/ssl_private.h
index 2a08d1c..8055200 100644
--- a/modules/ssl/ssl_private.h
+++ b/modules/ssl/ssl_private.h
@@ -655,10 +655,13 @@ typedef struct {
     const char  *cert_file;
     const char  *cert_path;
     const char  *ca_cert_file;
-    STACK_OF(X509_INFO) *certs; /* Contains End Entity certs */
-    STACK_OF(X509) **ca_certs; /* Contains ONLY chain certs for
-                                * each item in certs.
-                                * (ptr to array of ptrs) */
+    /* certs is a stack of configured cert, key pairs. */
+    STACK_OF(X509_INFO) *certs;
+    /* ca_certs contains ONLY chain certs for each item in certs.
+     * ca_certs[n] is a pointer to the (STACK_OF(X509) *) stack which
+     * holds the cert chain for the 'n'th cert in the certs stack, or
+     * NULL if no chain is configured. */
+    STACK_OF(X509) **ca_certs;
 } modssl_pk_proxy_t;
 
 /** stuff related to authentication that can also be per-dir */