diff --git a/R/PM_model.R b/R/PM_model.R
index 0ad33f20c..bf1e13560 100644
--- a/R/PM_model.R
+++ b/R/PM_model.R
@@ -1413,6 +1413,9 @@ PM_model <- R6::R6Class(
       }
 
       dir.create(path_run, recursive = TRUE)
+      # normalizePath() leaves a not-yet-existing path relative; make it absolute
+      # now, as the fit may run from the prior's temporary folder.
+      path_run <- normalizePath(path_run)
 
       #### Save input objects ####
       dir.create(normalizePath(file.path(path_run, "inputs"), mustWork = FALSE), recursive = TRUE)
diff --git a/tests/testthat/test-pm-fit-prior-run-path.R b/tests/testthat/test-pm-fit-prior-run-path.R
new file mode 100644
index 000000000..391998d3d
--- /dev/null
+++ b/tests/testthat/test-pm-fit-prior-run-path.R
@@ -0,0 +1,39 @@
+library(Pmetrics)
+
+test_that("PM_model$fit with numeric prior passes absolute paths when path is relative", {
+  withr::local_dir(withr::local_tempdir(pattern = "prior-relpath-"))
+
+  params <- tolower(names(NPex$model$model_list$pri))
+  dir.create(file.path("1", "outputs"), recursive = TRUE)
+  prior_df <- data.frame(matrix(0.5, nrow = 4, ncol = length(params), dimnames = list(NULL, params)), prob = 0.25)
+  utils::write.csv(prior_df, file.path("1", "outputs", "theta.csv"), row.names = FALSE)
+
+  model <- PM_model$new(x = NPex$model, compile = FALSE)
+
+  data_found <- NULL
+  captured_output <- NULL
+
+  testthat::with_mocked_bindings(
+    fit = function(model_source, data, params, output_path, solver = NULL) {
+      data_found <<- file.exists(data)
+      captured_output <<- output_path
+      dir.create(output_path, recursive = TRUE)
+      invisible(NULL)
+    },
+    PM_parse = function(path) invisible(NULL),
+    PM_load = function(path, file, ...) structure(list(path = path), class = c("PM_result", "R6")),
+    {
+      model$fit(
+        data = NPex$data,
+        run = 2,
+        cycles = 0,
+        prior = 1,
+        report = "none",
+        quiet = TRUE
+      )
+    }
+  )
+
+  expect_true(data_found)
+  expect_equal(captured_output, file.path(normalizePath("2"), "outputs"))
+})