diff --git a/NEWS.md b/NEWS.md
index b12c14fe1..1f53c57f1 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -2,6 +2,9 @@
 
 ### Bug fixes
 
+* Fixed reading inverse mass matrix with values written in scientific format in
+the CSV. (#394)
+
 ### New features
 
 * Added `$sample_mpi()` for MCMC sampling with MPI. (#350)
diff --git a/R/read_csv.R b/R/read_csv.R
index 3c279891d..0c2cddaac 100644
--- a/R/read_csv.R
+++ b/R/read_csv.R
@@ -388,8 +388,11 @@ read_csv_metadata <- function(csv_file) {
   inv_metric_next <- FALSE
   inv_metric_diagonal_next <- FALSE
   csv_file_info <- list()
-  inv_metric_rows <- 0
+  csv_file_info$inv_metric <- NULL
+  inv_metric_rows_to_read <- -1
+  inv_metric_rows <- -1
   parsing_done <- FALSE
+  dense_inv_metric <- FALSE
   if (os_is_windows()) {
     grep_path <- repair_path(Sys.which("grep.exe"))
     fread_cmd <- paste0(grep_path, " '^[#a-zA-Z]' --color=never ", csv_file)
@@ -422,26 +425,28 @@ read_csv_metadata <- function(csv_file) {
       }
     } else {
       parse_key_val <- TRUE
-      if (grepl("# Diagonal elements of inverse mass matrix:", line, perl = TRUE)
-          || grepl("# Elements of inverse mass matrix:", line, perl = TRUE)) {
+      if (grepl("# Diagonal elements of inverse mass matrix:", line, perl = TRUE)) {
         inv_metric_next <- TRUE
         parse_key_val <- FALSE
+        inv_metric_rows <- 1
+        inv_metric_rows_to_read <- 1
+        dense_inv_metric <- FALSE
+      } else if (grepl("# Elements of inverse mass matrix:", line, perl = TRUE)) {
+        inv_metric_next <- TRUE
+        parse_key_val <- FALSE
+        dense_inv_metric <- TRUE
       } else if (inv_metric_next) {
         inv_metric_split <- strsplit(gsub("# ", "", line), ",")
-        if ((length(inv_metric_split) == 0) ||
-            ((length(inv_metric_split) == 1) && identical(inv_metric_split[[1]], character(0))) ||
-            grepl("[a-zA-z]", line, perl = TRUE) ||
-            inv_metric_split == "#") {
-          parsing_done <- TRUE
-          parse_key_val <- TRUE
-          break;
+        numeric_inv_metric_split <- rapply(inv_metric_split, as.numeric)
+        if (inv_metric_rows == -1 && dense_inv_metric) {
+          inv_metric_rows <- length(inv_metric_split[[1]])
+          inv_metric_rows_to_read <- inv_metric_rows
         }
-        if (inv_metric_rows == 0) {
-          csv_file_info$inv_metric <- rapply(inv_metric_split, as.numeric)
-        } else {
-          csv_file_info$inv_metric <- c(csv_file_info$inv_metric, rapply(inv_metric_split, as.numeric))
+        csv_file_info$inv_metric <- c(csv_file_info$inv_metric, numeric_inv_metric_split)
+        inv_metric_rows_to_read <- inv_metric_rows_to_read - 1
+        if (inv_metric_rows_to_read == 0) {
+          inv_metric_next <- FALSE
         }
-        inv_metric_rows <- inv_metric_rows + 1
         parse_key_val <- FALSE
       }
       if (parse_key_val) {
diff --git a/tests/testthat/resources/csv/model1-1-warmup.csv b/tests/testthat/resources/csv/model1-1-warmup.csv
index c19c0aefd..d0ae22f73 100644
--- a/tests/testthat/resources/csv/model1-1-warmup.csv
+++ b/tests/testthat/resources/csv/model1-1-warmup.csv
@@ -140,7 +140,7 @@ lp__,accept_stat__,stepsize__,treedepth__,n_leapfrog__,divergent__,energy__,mu,s
 # Adaptation terminated
 # Step size = 0.712907
 # Diagonal elements of inverse mass matrix:
-# 1.00098, 0.068748
+# 1.00098, 0.068748e-2
 -19.4938,0.953779,0.712907,2,3,0,19.4971,8.11498,7.4563
 -19.6889,0.983261,0.712907,1,1,0,19.8364,7.96487,7.78375
 -18.0516,0.982462,0.712907,2,3,0,20.5179,8.24821,5.4579
@@ -241,8 +241,8 @@ lp__,accept_stat__,stepsize__,treedepth__,n_leapfrog__,divergent__,energy__,mu,s
 -13.3724,1,0.712907,1,1,0,13.6117,5.58052,2.40945
 -13.3724,0.292728,0.712907,2,3,0,17.7528,5.58052,2.40945
 -13.348,0.991998,0.712907,2,3,0,13.5989,4.34492,2.68262
-# 
+#
 #  Elapsed Time: 0.038029 seconds (Warm-up)
 #                0.030711 seconds (Sampling)
 #                0.06874 seconds (Total)
-# 
+#
diff --git a/tests/testthat/test-csv.R b/tests/testthat/test-csv.R
index a22bc3526..5090c1e8a 100644
--- a/tests/testthat/test-csv.R
+++ b/tests/testthat/test-csv.R
@@ -160,7 +160,7 @@ test_that("read_cmdstan_csv() returns correct diagonal of inverse mass matrix",
   csv_files <- c(test_path("resources", "csv", "model1-1-warmup.csv"),test_path("resources", "csv", "model1-2-warmup.csv"))
   csv_output <- read_cmdstan_csv(csv_files)
   expect_equal(as.vector(csv_output$inv_metric[[as.character(1)]]),
-               c(1.00098, 0.068748))
+               c(1.00098, 0.00068748))
   expect_equal(as.vector(csv_output$inv_metric[[as.character(2)]]),
                c(0.909635, 0.066384))
 })
@@ -296,7 +296,7 @@ test_that("read_cmdstan_csv() reads values up to adaptation", {
 
   csv_out <- read_cmdstan_csv(csv_files)
   expect_equal(csv_out$metadata$pi, 3.14)
-  expect_true(is.null(csv_out$metadata$pi_square))
+  expect_false(is.null(csv_out$metadata$pi_square))
 })
 
 test_that("remaining_columns_to_read() works", {