diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c
index e3fa4390f8460685c0bd57fe8d52c9c043de719f..4ddbf6604e2abf13e5c2725392ce4213de691d8c 100644
--- a/drivers/edac/ghes_edac.c
+++ b/drivers/edac/ghes_edac.c
@@ -189,6 +189,7 @@ void ghes_edac_report_mem_error(struct ghes *ghes, int sev,
 	/* Cleans the error report buffer */
 	memset(e, 0, sizeof (*e));
 	e->error_count = 1;
+	e->grain = 1;
 	strcpy(e->label, "unknown label");
 	e->msg = pvt->msg;
 	e->other_detail = pvt->other_detail;
@@ -284,7 +285,7 @@ void ghes_edac_report_mem_error(struct ghes *ghes, int sev,
 
 	/* Error grain */
 	if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK)
-		e->grain = ~(mem_err->physical_addr_mask & ~PAGE_MASK);
+		e->grain = ~mem_err->physical_addr_mask + 1;
 
 	/* Memory error location, mapped on e->location */
 	p = e->location;
@@ -391,8 +392,13 @@ void ghes_edac_report_mem_error(struct ghes *ghes, int sev,
 	if (p > pvt->other_detail)
 		*(p - 1) = '\0';
 
+	/* Sanity-check driver-supplied grain value. */
+	if (WARN_ON_ONCE(!e->grain))
+		e->grain = 1;
+
+	grain_bits = fls_long(e->grain - 1);
+
 	/* Generate the trace event */
-	grain_bits = fls_long(e->grain);
 	snprintf(pvt->detail_location, sizeof(pvt->detail_location),
 		 "APEI location: %s %s", e->location, e->other_detail);
 	trace_mc_event(type, e->msg, e->label, e->error_count,