diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 2181a39853..ea54d164cc 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -5669,9 +5669,23 @@ set_config_option(const char *name, const char *value,
 				 * ignore it in existing backends.	This is a tad klugy, but
 				 * necessary because we don't re-read the config file during
 				 * backend start.
+				 *
+				 * In EXEC_BACKEND builds, this works differently: we load all
+				 * nondefault settings from the CONFIG_EXEC_PARAMS file during
+				 * backend start.  In that case we must accept PGC_SIGHUP
+				 * settings, so as to have the same value as if we'd forked
+				 * from the postmaster.  We detect this situation by checking
+				 * IsInitProcessingMode, which is a bit ugly, but it doesn't
+				 * seem worth passing down an explicit flag saying we're doing
+				 * read_nondefault_variables().
 				 */
+#ifdef EXEC_BACKEND
+				if (IsUnderPostmaster && !IsInitProcessingMode())
+					return -1;
+#else
 				if (IsUnderPostmaster)
 					return -1;
+#endif
 			}
 			else if (context != PGC_POSTMASTER && context != PGC_BACKEND &&
 					 source != PGC_S_CLIENT)
@@ -8310,6 +8324,12 @@ read_nondefault_variables(void)
 	GucSource	varsource;
 	GucContext	varscontext;
 
+	/*
+	 * Assert that PGC_BACKEND case in set_config_option() will do the right
+	 * thing.
+	 */
+	Assert(IsInitProcessingMode());
+
 	/*
 	 * Open file
 	 */