diff --git a/src/opm/io/eclipse/ERsm.cpp b/src/opm/io/eclipse/ERsm.cpp
index d0839de9f..2e4336de3 100644
--- a/src/opm/io/eclipse/ERsm.cpp
+++ b/src/opm/io/eclipse/ERsm.cpp
@@ -22,6 +22,8 @@
 #include <cmath>
 #include <chrono>
 
+#include <fmt/format.h>
+
 #include <opm/io/eclipse/ERsm.hpp>
 #include <opm/io/eclipse/ESmry.hpp>
 #include <opm/common/utility/FileSystem.hpp>
@@ -255,21 +257,29 @@ bool cmp(const ESmry& smry, const ERsm& rsm) {
     const auto& summary_dates = smry.dates();
     if (rsm.has_dates()) {
         const auto& rsm_dates = rsm.dates();
-        if (rsm_dates.size() != summary_dates.size())
+        if (rsm_dates.size() != summary_dates.size()) {
+            fmt::print(stderr, "len(summary) = {}    len(rsm) = {}", summary_dates.size(), rsm_dates.size());
             return false;
+        }
 
         for (std::size_t time_index = 0; time_index < rsm_dates.size(); time_index++) {
             const auto smry_ts = TimeStampUTC( std::chrono::system_clock::to_time_t(summary_dates[time_index]) );
             const auto rsm_ts = rsm_dates[time_index];
 
-            if (smry_ts.year() != rsm_ts.year())
+            if (smry_ts.year() != rsm_ts.year()) {
+                fmt::print(stderr, "time_index: {}  summary.year: {}   rsm.year: {}", time_index, smry_ts.year(), rsm_ts.year());
                 return false;
+            }
 
-            if (smry_ts.month() != rsm_ts.month())
+            if (smry_ts.month() != rsm_ts.month()) {
+                fmt::print(stderr, "time_index: {}  summary.month: {}   rsm.month: {}", time_index, smry_ts.month(), rsm_ts.month());
                 return false;
+            }
 
-            if (smry_ts.day() != rsm_ts.day())
+            if (smry_ts.day() != rsm_ts.day()) {
+                fmt::print(stderr, "time_index: {}  summary.day: {}   rsm.day: {}", time_index, smry_ts.day(), rsm_ts.day());
                 return false;
+            }
         }
     } else {
         const auto& rsm_days = rsm.days();
@@ -281,8 +291,10 @@ bool cmp(const ESmry& smry, const ERsm& rsm) {
             using TP      = time_point<system_clock>;
             auto smry_days = duration_cast<TP::duration>(summary_dates[time_index] - summary_dates[0]).count() / 86400.0 ;
 
-            if (!cmp::scalar_equal(smry_days, rsm_days[time_index]))
+            if (!cmp::scalar_equal(smry_days, rsm_days[time_index])) {
+                fmt::print(stderr, "time_index: {}  summary.days: {}   rsm.days: {}", time_index, smry_days, rsm_days[time_index]);
                 return false;
+            }
         }
     }
 
@@ -313,8 +325,10 @@ bool cmp(const ESmry& smry, const ERsm& rsm) {
             const double diff = static_cast<double>(smry_vector[index]) - rsm_vector[index];
             const double sum = std::fabs(static_cast<double>(smry_vector[index])) + std::fabs(rsm_vector[index]);
 
-            if (diff > 1e-5 * sum)
+            if (diff > 1e-5 * sum) {
+                fmt::print(stderr, "time_index: {}  key: {}  summary: {}   rsm: {}", index, key, smry_vector[index], rsm_vector[index]);
                 return false;
+            }
         }
     }