diff --git a/packer/core.go b/packer/core.go
index 507c79b81..c9672eb96 100644
--- a/packer/core.go
+++ b/packer/core.go
@@ -3,6 +3,7 @@ package packer
 import (
 	"fmt"
 	"sort"
+	"strings"
 
 	ttmp "text/template"
 
@@ -366,9 +367,13 @@ func (c *Core) init() error {
 				c.variables[k] = renderedV
 				ctx.UserVariables = c.variables
 			case ttmp.ExecError:
-				shouldRetry = true
-				failedInterpolation = fmt.Sprintf(`"%s": "%s"`, k, v)
-				continue
+				castError := err.(ttmp.ExecError)
+				if strings.Contains(castError.Error(), interpolate.ErrVariableNotSetString) {
+					shouldRetry = true
+					failedInterpolation = fmt.Sprintf(`"%s": "%s"; error: %s`, k, v, err)
+				} else {
+					return err
+				}
 			default:
 				return fmt.Errorf(
 					// unexpected interpolation error: abort the run
diff --git a/template/interpolate/funcs.go b/template/interpolate/funcs.go
index 57495052a..1d76f8f06 100644
--- a/template/interpolate/funcs.go
+++ b/template/interpolate/funcs.go
@@ -47,6 +47,8 @@ var FuncGens = map[string]FuncGenerator{
 	"lower": funcGenPrimitive(strings.ToLower),
 }
 
+var ErrVariableNotSetString = "Error: variable not set:"
+
 // FuncGenerator is a function that given a context generates a template
 // function for the template.
 type FuncGenerator func(*Context) interface{}
@@ -168,7 +170,7 @@ func funcGenUser(ctx *Context) interface{} {
 			// error and retry if we're interpolating UserVariables. But if
 			// we're elsewhere in the template, just return the empty string.
 			if !ok {
-				return "", errors.New(fmt.Sprintf("variable %s not set", k))
+				return "", fmt.Errorf("%s %s", ErrVariableNotSetString, k)
 			}
 		}
 		return val, nil