diff --git a/prometheus.scm b/prometheus.scm
index d6caa6a..f6e4c23 100644
--- a/prometheus.scm
+++ b/prometheus.scm
@@ -291,10 +291,13 @@ To specify values for the labels, pass an alist as
 values are the values."
   (unless (memq (metric-type metric)
                 '(counter gauge))
-    (error "can only increment counter and gauge metrics"))
+    (raise-exception
+     (make-exception-with-message
+      "can only increment counter and gauge metrics")))
 
   (unless (positive? by)
-    (error "can only increment positive values"))
+    (raise-exception
+     (make-exception-with-message "can only increment positive values")))
 
   (let ((canonical-labels
          (canonicalise-label-values label-values))
@@ -322,7 +325,8 @@ To specify values for the labels, pass an alist as
 values are the values."
   (unless (memq (metric-type metric)
                 '(gauge))
-    (error "can only increment gauge metrics"))
+    (raise-exception
+     (make-exception-with-message "can only increment gauge metrics")))
 
   (let ((canonical-labels
          (canonicalise-label-values label-values))
@@ -348,7 +352,8 @@ To specify values for the labels, pass an alist as
 values are the values."
   (unless (memq (metric-type metric)
                 '(gauge))
-    (error "can only set gauge metrics"))
+    (raise-exception
+     (make-exception-with-message "can only set gauge metrics")))
 
   (unless (number? value)
     (raise-exception
@@ -374,7 +379,9 @@ To specify values for the labels, pass an alist as
 values are the values."
 
   (unless (histogram-metric-type? (metric-type metric))
-    (error "can only observe histogram metrics"))
+    (raise-exception
+     (make-exception-with-message
+      "can only observe histogram metrics")))
 
   (let ((canonical-labels
          (canonicalise-label-values label-values))