diff --git a/NEWS.md b/NEWS.md
index 3da3e51f..d6190938 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,8 @@
 # ellmer (development version)
 
+* `chat_claude()` and `chat_bedrock()` no longer choke after receiving an 
+  output that consists only of whitespace (#376).
+
 * `live_browser()` now initializes `shinychat::chat_ui()` with the messages from
   the chat turns, rather than replaying the turns server-side (#381).
 
diff --git a/R/provider-bedrock.R b/R/provider-bedrock.R
index 58466cd1..44854997 100644
--- a/R/provider-bedrock.R
+++ b/R/provider-bedrock.R
@@ -284,7 +284,11 @@ method(as_json, list(ProviderBedrock, Turn)) <- function(provider, x) {
 }
 
 method(as_json, list(ProviderBedrock, ContentText)) <- function(provider, x) {
-  list(text = x@text)
+  if (is_whitespace(x@text)) {
+    list(text = "[empty string]")
+  } else {
+    list(text = x@text)
+  }
 }
 
 method(as_json, list(ProviderBedrock, ContentImageRemote)) <- function(
diff --git a/R/provider-claude.R b/R/provider-claude.R
index 06dbda88..94257dbf 100644
--- a/R/provider-claude.R
+++ b/R/provider-claude.R
@@ -266,7 +266,11 @@ method(as_json, list(ProviderClaude, Turn)) <- function(provider, x) {
 }
 
 method(as_json, list(ProviderClaude, ContentText)) <- function(provider, x) {
-  list(type = "text", text = x@text)
+  if (is_whitespace(x@text)) {
+    list(type = "text", text = "[empty string]")
+  } else {
+    list(type = "text", text = x@text)
+  }
 }
 
 method(as_json, list(ProviderClaude, ContentPDF)) <- function(provider, x) {
diff --git a/R/utils.R b/R/utils.R
index 2e8e608b..99fdd8ce 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -128,3 +128,7 @@ modify_list <- function(x, y) {
 
   utils::modifyList(x, y)
 }
+
+is_whitespace <- function(x) {
+  grepl("^(\\s|\n)*$", x)
+}
diff --git a/tests/testthat/test-provider-bedrock.R b/tests/testthat/test-provider-bedrock.R
index c2300f00..6ca5df48 100644
--- a/tests/testthat/test-provider-bedrock.R
+++ b/tests/testthat/test-provider-bedrock.R
@@ -72,6 +72,13 @@ test_that("can use pdfs", {
   test_pdf_local(chat_fun)
 })
 
+# Provider idiosynchronies -----------------------------------------------
+
+test_that("continues to work after whitespace only outputs (#376)", {
+  chat <- chat_bedrock()
+  chat$chat("Respond with only two blank lines")
+  expect_equal(chat$chat("What's 1+1? Just give me the number"), "2")
+})
 
 # Auth --------------------------------------------------------------------
 
diff --git a/tests/testthat/test-provider-claude.R b/tests/testthat/test-provider-claude.R
index edcabcba..1171c496 100644
--- a/tests/testthat/test-provider-claude.R
+++ b/tests/testthat/test-provider-claude.R
@@ -62,3 +62,9 @@ test_that("can set beta headers", {
   req <- chat_request(provider)
   expect_equal(req$headers$`anthropic-beta`, c("a", "b"))
 })
+
+test_that("continues to work after whitespace only outputs (#376)", {
+  chat <- chat_claude()
+  chat$chat("Respond with only two blank lines")
+  expect_equal(chat$chat("What's 1+1? Just give me the number"), "2")
+})
diff --git a/tests/testthat/test-utils.R b/tests/testthat/test-utils.R
index 79c5cc73..2f902915 100644
--- a/tests/testthat/test-utils.R
+++ b/tests/testthat/test-utils.R
@@ -10,3 +10,11 @@ test_that("informative error if no key", {
   expect_false(key_exists("FOO"))
   expect_snapshot(key_get("FOO"), error = TRUE)
 })
+
+test_that("detects whitespace", {
+  expect_true(is_whitespace("\n\n\n \t"))
+  expect_true(is_whitespace(""))
+
+  expect_false(is_whitespace("a"))
+  expect_false(is_whitespace("."))
+})